What would be the right topper for my mattress?

I have a very hard mattress due to mine and my husband's weight which is combined 46 stone. I need a topper as I have fibromyalgia, and a very painful frozen shoulder. At the moment I have a gel topper but I don't feel it gives the right support as very soft. I am 21 stone and due to my lack of flexibility struggle to get out of bed. I also have diabetes and have to get up a lot during the night. The topper is just for my side as hubby ver comfortable.