I'm 58 and 80 pounds overweight. I use a raised prostration board. I stand on the floor and the board raised 4". That helps in the part of the exercise where you push up to return to the standing position. It makes it much easier, like 40% easier. It is usually frowned upon, but since I'm old I got special permission, and that from a really tough no-compromise lama. Knee pads taped to the board help with the impact.
But you know your situation. Whatever you do in this regard, or don't do, don't let it become an impediment to practice. Better to do what you honestly can than to be a purist and don't do anything at all.
Speaking of prostrations, I recommend to everybody that they get a swimmer's lap counter. You put it on your finger and click it every prostration. It's so much nicer than the hand mala, or even worse, a full mala!
A human being has his limits. And thus, in every conceivable way, with every possible means, he tries to make the teaching enter into his own limits. ChNN