Best mattress type for me

Hi, my name is Magdalena I'm 25 and suffer from lower back pains mainly, but also upper back and pelvis.

I'm 5'9 tall about 10 stone maybe a bit less (62kg). I'm looking for a double size bed with a mattress that will support my back. I have looked up every mattress type and I'm still confused on which one to buy?

Please help me with the decision? I don't want to go over £1000 ideally cheaper. Thank you
Kind regards,
Magdalena