I have a lot of the same limitations! I chuckled when I read your list in those last couple of sentences! So many think well, if it's just a sitting job, should be no problem, right? Wrong!!
I still think you can be working a couple of hours (has more to do with whether it matches what you say your limitations are, and how much you earn, but I could be wrong on all this). Anyway, maybe straydog will weigh in. What I read on the SSD site when I started digging had to do with the inability to work and that was defined as "gainful employment", along with a few other terms. And if you were making more than $900/month that would disqualify you, but you could be working and making less. At least that's how I read it.
And it's such a difference working a full day, 5 day week than just working a couple of hours here or there. BIG difference!