A family member made one with an exoskeleton to hold it all together (separate foam blocks, four for the base with a firm block under a soft one for structure, raised sides and full block for the back with a tube cage to hold them all together) that lasted more than 40 years with only one reupholster.

The foam blocks were quite cheap direct from the supplier (I think they made mattresses, the back plate was an offcut but the rest were practically custom)

If you can get yourself some decent foam blocks then it could be more cost effective and long lasting to make your own using fabric to hold the shape together the way store bought ones do.