I am a long time Buddhist practitioner in the Tibetan traditions and Soto Zen. Over the years I have had to adapt my practices and most of the time now I 'sit' laying down. I also lead ceremony and practice online sitting up rather than standing - meditation, chanting, Tonglen and Ryaku Fusatsu (the Zen version of the full moon Uposatha ceremony).
I wrote a little about practicing with illness and disability, and lead that side of practice at my sangha: https://andykokuumclellan.wordpress.com/practicing-zen-with-illness-disability/
That also includes a list of resources of practicing with illness, and the website has a link to my audio recordings of some traditional Buddhist and Zen teachings, and suggested online sits and podcasts of dharma teachings.
For me, Buddhism is about accepting where we are for now, even as we work to get better. I have not yet found any magic mantras or practices for healing, including in varayana, but I can only speak for myself in that.
This moment, right here and right now, has nothing missing or left out. Illness does not mean that something has gone wrong, it is a natural part of life, just as are birth and death. However, it would be wrong to say that chronic illness does not create a huge amount of suffering, and anything we can do to reduce this, both in ourselves and others, has to be a good thing.
With much metta
ps. my You Tube channel has a guided breath awareness meditation
and a body scan meditation
. I hope to have a guided tonglen and metta practice and some resources on that soon.