We have stores that sell used office furniture and you may be able to find a doctor stool there. I was at an Estate sale and saw a wonderful chair for $20 that had several adjustments on it. The fabric was like new.
Also, go to Home Depot or Lowe's and get a wood shop stool, cut the legs down to the height you want, drill a hole in the bottom of each leg and add wheels. I like a back on my chair that gives me support. Also, some stores like Bed n Bath have bathroom stools that wheels can be put on. If you find a chair that is a little too low, make a cushion from thick foam and cover it, will add to the deco of the room.
I'm real picky on my chairs and only use office chairs that I can adjust the height and back and has at least 5 wheels. You only have one back and as you get older it's really important to take care of it or you will be paying the doctor's more than what a good chair cost.