Can I buy a Half bed mattress topper?

[Thingsthatgo]

I love our mattress. I find it so comfortable, like sleeping on a cloud. It's a really deep, really soft mattress. (I always thought I like firm mattresses until I tried this one).
Anyway, DH likes a firm mattress, and is complaining about getting a sore back.
Before I kiss goodbye to my cloud bed, can we do something else? Can I get a half king size bed topper that will firm up his half?

Bump

Get a single bed one ?

@mrsDracoMalfoy thanks. I've never used one before. Would a single one stay in one place do you think? Or move around.

Hmmm I'm not sure either, I've never used one. You could possibly look at some straps from top to bottom to keep it in place 🤷🏽‍♀️