Hi April,

Sorry, your husband is struggling with his firm side, a lot of people struggle with firm mattresses. Too firm and its like sleeping on a board.

I'm afraid you can't replace once half of a zip and link. They are matched up during manufacture to make sure the zips line up exactly. Every mattress is also a different depth so there's no way that two different models would match up.

You could simply pair up a single mattress next to it but again the size difference would be noticeable and rather unpractical. So we wouldn't recommend that either.

If you can let us know your weights and heights we can help give you some recommendations as to which models may be suitable.

Sorry, we can't be of more help April!