Two twin mattresses when laid side by side on an extended ikea daybed are about 5” shorter than a king bed. I am thinking of buying an ikea daybed with 2 thin spring mattresses as recommended, then also getting a 3” king sized foam mattress topper.

The trick is that I’ll add a removable 5” wood extension off the end of the bed so the mattress topper can be laid out at full king size, including with king size fitted sheets. The 5” extension will be raised by about 3” from the height of the bed slats so it matches up well enough with a single thin mattress that’s in use, and have a 3” lip so that it looks good with king size fitted sheets wrapped around it. The 3” topper should also eliminate the feel of a gap between the spring mattresses.

That’s the concept at least. We have tall people in our family and want a real king size guest bed with a thick mattress, and I figure 3” foam plus 5” spring will be real enough. Before I buy everything, has anybody else tried something similar? Is this idea genius or stupid?