New mattress too soft - topper help?

[biscuitdunkerette]

Turns out DH and I have differing needs in a mattress. I’m finding our £££ new one just not supportive enough and wake up with a sore back. He’s finding it grand. .
I’ve searched and mattress toppers seem to be about making firm mattresses softer, but is there a kind that can give me more firm support? Latex?
We have a Superking so was thinking of getting a single size for just my side.

Surely you can send the mattress back? Bed shops nowadays always seem to offer the assurance that if it’s not comfortable within a certain period of time you can return it.

Unfortunately not an option at this stage. We’ve tried! So a topper is the best solution I can think of, though they all seem soft.