I recently started learning the piano as an adult, and from what i've gathered from reading and watching videos, the 'folk wisdom' about how to avoid rsi-type injuries is to minimize tension in your wrist by maximizing relaxation of your fingers and wrists (especially the thumbs, which tend to get locked into a permanent state of mild tension on the piano keyboard). So you want to do your best to develop more finger independence, so that you can press with one finger while keeping the neighboring fingers relaxed. It's really hard.
If you can I'd recommend getting piano teacher and live lessons. I got one and improvement in posture was a biggest gain I got. That and some cultural push (e.g. there's no wrong music, only the music someone doesn't like, or put piano next to window to learn to not watch on own hands).
I’ve thought quite a bit about getting a teacher, but have hesitated for a few [somewhat legitimate] reasons. Among them, I’m partially disabled and can’t practice consistently. However, having a teacher berate me about my posture would actually probably help that at least a little bit, now that you mention in :-) Thanks for taking the time to share your experience and encouragement with me! Best of luck on your lessons as well.
