I generally advise against sit-to-stand anything that is pricey, except things like a lift chair that can still be used with a Hoyer, because the core and upper body strength can go very quickly, making such equipment uncomfortable and risky.
Ultimately he will need to toilet using a Hoyer lift. If you can help him stand for now, or if an elevated toilet riser (not expensive) is sufficient for him to get his legs under him, those are both options. But I wouldn't install it permanently for the reason above -- you will ultimately want to fit a shower/commode chair or Hoyer over the toilet, instead of the riser, if you have room in your bathroom.