I do not think this is silly at all. I responded to a young POTS sufferer earlier who was having a hard time with a lack of understanding and support from their parents. Seeing your post brings me a sense of relief and gratitude that you are being so proactive.

I am a Buddhist and POTS patient, and upright meditation can be difficult for me. I purchased this chair: https://www.amazon.com/gp/product/B09B3NZRX9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It is very comfortable- certainly more so than sitting on the floor (for me anyway)- and I really like that it can lock in different positions.

As for actual chairs: anything that is low enough to allow me to keep my thighs up off the edge of the chair and my knees slightly elevated is usually all right for a while.

Recliners are wonderful, or something in which they can curl their legs up under them. Big throw pillows are nice, too. I have these for meditation, but they’re ideal for lounging and sprawling: https://www.amazon.com/gp/product/B08WCD75LP/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I wish you all the best, and hope you are all able to get an appropriate diagnosis swiftly! 😊