Here’s how we built ours: https://www.frugalfamilytimes.com/2013/05/how-to-build-raised-garden-bed-boxes.html
My son used some pallets he took apart to make some raised beds. But if you can't bend over you might have difficulty building one. I have seem several advertised by home depot and Lowes that you basically just open and set up. Good luck. Oh, the one my son made is 4 x4 x 3. It took 14 bags of soil to fill it. We have another one now which is 8x4x12 and estimate it will take 40 cubic yards to fill it.