Any input is welcome, as its something I've kind of inherited - hence my uncertainty about delving too deeply.
But I'm thinking 2. above shouldn't get too messy :
1. Add a field CushionID to the main Products table.
2. Add a Cushions table.
3. On the Product Details page add a new recordset to show the Cushion where Cushions_CushionID = Products_CushionID.
4. Include a link to that Product's details page.
Does that sound about right?