okay, my little sister has scoliosis, and she’s had several back surgeries. I told her a while back, because of that she doesn’t really need to kneel in church, but do show some sort of active reverence, not to be fair she does anyway. But if you’re incapable of doing stuff like that from more than a little bit at a time, You’re more than welcome to sit down. If you’re able to though, I still think it wise to stand at the gospel and kneel at the consecration. if you’re physically unable to do that, try to show some other sign of veneration. I’m about the same age, and I have some medical problems of my own, because of spinal damage I had from when I was younger, I have a hard time genuflecting, you would think it would be my knees that would be more of an issue in preventing that. So, I adopted the Eastern Christian habit of venerating the altar by bowing. Again, if you’re not able to do that, or your non-Catholic background makes you uncomfortable doing that, find some other way to express it. You and I are around the same age, so happy birthday, although mine was earlier this year, and I hope I’ve been of help