I have had to try to move my practice to other areas of my life, as "sitting zen" has been a problem for me of late, since it was extremely painful to set in any of the positions for a long time. Yes, including a chair.
I have now had surgery to repair a torn meniscus. It is amazing that this is a relatively straightforward operation these days (costing about as much as a first class intercontinental air fare, in case you're interested). Hopefully within a few weeks I'll be right as rain.
If you have such an operation it gives that whole merit thing a whole new perspective. Look, if you can sit, great. If you can penetrate through the Great Matter, great. But don't pretend that any merit you'd gain this way is better than those for whom such effort is a real tribulation because of physical limitations or economic limitations or family commitments. It just isn't.
There is a Great Matter to be penetrated, there is a world hurting to be in the midst of a practice of deep love and compassion, but please don't pretend your practice is better than any greedy person's shiny new toys bought with alienated labor, because you're just making that practice into a shiny new toy.