Zip & link, is there such a thing as a 4' 6" and not Kingsize?

Delight to find an honest website and approach to buying a new bed/mattress. After many years we've decided we need a separate mattress system for our double bed. My wife is half my weight at about 7st while I am just over 14st! We sleep on opposite body sides, my being on my RH side as a rule usually changing overnight. If I sleep on my back I snore! Our current mattress is 15 years old and no it will come as no surprise since about age 55 I am at 61 now having recurring back and hip problems. We are desperate to find a suitable combination for each of us, my preference is for a firmish mattress while my wife likes a softer type.
I know a new mattress is needed as we swapped a new mattress from our spare double bed and I slept well for the first time in years but my wife did not!
What advice can you give us please.
Malcolm
Wool, Dorset