Menopausal lady with some lower back pain

Dear John Ryan, I wanted some advice as to what may be the best mattress for me. I am a female in my early 50’s who weights 12.3 stone and sleeps alone. A few years ago I had lower back pain which has now improved significantly; I keep it at bay with yoga and visits to a chiropractor, but my back does ache a little every morning when I wake up. My mattress is old and I fear it is not helping my back and may even be the cause of the slight back ache I have on waking..I am also menopausal and get hot flushes, so have to fling off my duvet for some minutes a few times every night, but this doesn’t really affect my sleep much.I would be grateful for any advice/recommendations.. I can only afford the lower end budget-wise I am afraid, but am impressed by your website and all the positive recommendations.. Thanking you in advance