Praise be to Allah.
We ask Allah to both reward you as well as grant you well-being and to grant you patience in the face of what you have been tested with. We commend you on your great ambition in search of deeds which will earn you extra rewards and draw you closer to Allah, the Exalted, even while you are suffering from this sickness. Your illness has not prevented you from doing that which you can from acts of obedience and worship which have great rewards and weigh heavily on the balance. This is an important message we direct towards all those who are ill; that they should have such great ambition and not allow their sicknesses to prevent them from competing with the healthy in earning rewards.
With regard to the reward for what Allah, may He be exalted, has tested you with, we say: The scholars have differed as to whether the reward is granted merely due to the fact that Allah, may He be exalted, has tested His Muslim slave with sickness and calamity or is it a condition that it must be accompanied with patience and hope for reward. To explain that: calamities are an expiation for the afflicted as long as they do not show anger or tear their garments or lament, and they are a means of elevating one’s status and a source of rewards if the afflicted is patient and anticipates rewards (from Allah).
Al-Hafith ibn Hajar (may Allah have mercy on him) said: “The authentic reports are clear that rewards are established simply by a calamity occurring; as for patience and acceptance, then this is something extra for which one may be rewarded beyond the reward of the calamity. Al-Qarafi said: “Calamities are an expiation with certainty whether accompanied by patience or not. However, if accompanied by acceptance the expiation is greater, otherwise it will be less.” That’s what he said and the explanation is: A calamity is an expiation for a sin similar to it and through acceptance one is rewarded for it. If the afflicted has no sins, he will be compensated with rewards equal to it.” End quote from Fath al-Bari (10:105).
Sh. Muhammad ibn Salih al-‘Otheimin (may Allah have mercy on him) said: “Let the one afflicted with any calamity know that these calamities are an expiation for sins they committed; for no worry or anxiety or harm befalls a believer except that Allah expiates them (sins) through them (hardships), even a thorn which pricks them. Through patience and anticipation of reward one attains the level of the saabireen (patient ones), that high level about which Allah, may He be exalted, said (what means): “And We will surely test you with something of fear and hunger and a loss of wealth and lives and fruits, but give good tidings to the patient, Who, when disaster strikes them, say, "Indeed we belong to Allah, and indeed to Him we will return."” End quote.
This is the opinion favoured by the two sheikhs, Ibn Taimiyah and Ibn al-Qayyim (may Allah have mercy on them) and they mentioned shar’ee (Legal Islamic) evidences for that.
Know-dear questioner- that the time for qiyam al-layl (the voluntary night prayers) begins from after ‘Isha, and whether you pray in the first part of the night, the middle part or the last part of it, it is all part of qiyam al-layl and it was all done by the Prophet (may the peace and blessings of Allah be upon him). ‘Aisha (may Allah be pleased with her) said: “In every portion of the night did the Messenger of Allah (may the peace and blessings of Allah be upon him) do the witr (prayer)…the first part, the middle part and the last part of it, and his witr would go to the last sixth part (sahar).” Al-Bukhari and Muslim
Jabir (may Allah be pleased with him) said; The Messenger of Allah (may the peace and blessings of Allah be upon him) said: “Whoever fears not getting up in the last part of the night, let him do the witr in the first part and whoever expects he will get up in the last part of it let him do the witr at the end of the night. The prayer in the last part of the night is witnessed and that is better.” Muslim
Sh. ‘Abdul ‘Aziz ibn Baz (may Allah have mercy on him) said: “A person should pray as is convenient for him in the first part of the night or the middle part or the last part of it; he remains awake and prays as is made easy for him, supplicates to his Lord, turns towards Him, and seeks refuge with Him and he says the salam after every two units… The tahajjud (night prayer) in the first part of the night or the middle part or the last part of it is all good. However, the best is in the last part of the night if that is easy for him.” End quote.
As with regard to your request to guide you to deeds which are easy for you to do with your illness and which will not be burdensome and harmful for you to do and its rewards from Allah, the Mighty and Majestic, are plentiful, then this is a sign of your intelligence and high motivation. We ask Allah to grant you the strength to carry out these great acts of obedience. We do not see anything more fitting for you, due to your illness, than the words of remembrance which bring about great rewards from the Lord of the worlds if said. ‘Abdullah ibn Busr (may Allah be pleased with him) narrated that a man said: O Messenger of Allah, the laws of Islam have become many for me, tell me something I can cling to. He said: “Your tongue should remain moist with the remembrance of Allah.” At-Tirmithee, Ibn Majah and others. Authenticated by al-Albani.
Note that you may do great things -even with your sickness- such as inviting towards Allah, maintaining family ties (even via telephone) and buying booklets and having them distributed. We also bring your attention to the great rewards in good conduct which is the heaviest thing on the scale and which will elevate a person to the level of one who spends his time praying and fasting. So do not let your illness be an obstacle in carrying out those deeds which are not burdensome on you.
With regard to the books that guide you to what you have asked about, then you may read the book on this link: http://www.al-mostafa.info/data/arabic/depot2/gap.php?file=018040.pdf
Also the book:
The following article is also very beneficial:
Also see the answer to the question 174947.
May Allah grant you the ability to act upon what they contain
And Allah knows best.