Get the cheapest toilet seat and four short, wooden legs from the nearest home improvement center. Remove the rubber bumpers from the underside of the seat and attach the legs. Presto, rimming seat.
You can almost alwys find a protable commode at any used shop - 'junk' shop, flea market, etc. No work but to remove the pot and have at it. Most of them even have adjustable height legs...and you can always use a big pillow or cushion to get just the right height.