Back pain - bed or mattress?

[RMarieClaire]

Not sure where to post this but here goes. Last year we bought a new, slatted king sized bed from Simba plus a mattress from Eve. It was heaven. But, Unfortunately after a while DH didn't get on with the memory foam so we returned the mattress. In the end we bought a pocket sprung mattress from Dreams. We have the same mattress in our spare room but a double.

However we're really not comfortable in the bed. Both of us wake up with back pain, and we've spent the last few months mostly on the spare bed.

Could it be the bed causing issues, since the mattress brand (Beaumont K) and make is fine on our double? Or should we just accept it's the mattress?

We can't return it, and it was about £800. The bed was less than £300 and could be sold. I thought maybe about getting a Divan but don't want to throw away a couple of hundred if it's the mattress. Gah!