Mattress topper to make a mattress firmer? (Back pain)

[hallucinatingmaybe]

As above - we have a medium firm mattress that, while feeling wonderful if you're just sitting on it, leaves me with back and hip pain after a few nights on it (I have an existing bad back that the mattress is exacerbating). However, husband loves it and hates firm mattresses.

I've seen various toppers online that purport to give orthopaedic support and add firmness to a soft mattress which I think could be a happy compromise, but don't want to spend £££ on the strength of marketing claims alone ;)

Any recommendations?

We got one for DW who says it made a real difference to her back. However, my DF got just as good a result, he says, from getting a board from the local DIY store and putting it under the matress. Cost half the price.