Is your doc SURE it is the sesamoids causing the problem, not the replacement? I have to say my foot doc won't do replacement big toe joints if you want to be active. He says they are simply not robust enough to cope with the stress they get placed under and quickly fail. I had a 1st MTP fusion in April. I am 42 and fit and active. I have had some complications that have had nothing to do with the fusion itself, and I could not be happier with the fusion results. I don't limp, the toe is fused at a perfect angle for me to toe off and even to wear a low heel, and I cannot feel the hardware. You must get a surgeon who does a lot of these, understands your foot inside and out and can deal with complications should they happen. I can even stand on kind of tip toe, do push ups with weight through the big toe, and walk fast. None of my difficulties now come from the actual fusion!
I'd be seeking a second opinion. I can see why accessory sesamoids may cause issues but I have also read a huge amount about replacement big toe joints causing more pain than they solve....
Good luck. Foot pain sucks, I feel for you,