Having owned an Achilles IK and a few AIRE IK’s, I’m thinking the best results, while trying to save some money, would be to copy the use of AIRE’s older IK’s using firm foam floors (before they started using I-beam floors). Their single IK used a 2-piece foam floor and their double IK used a 3-piece foam floor. Essentially, the floors were of a certain thickness and deeply beveled around the edge-perimeter to tuck under and in to side-tube/floor cleavage.
The downside would be a little bulkier to store and transport.
The upside would be a firmer more responsive boat and drier on the butt, but primarily cheap and you’re able to get a precise fit.
I would attempt to find someone with another Achilles and see if you or them could trace their floor on a large piece of paper/clear plastic and measure the thickness. Use this as a pattern cut out a foam floor and then bevel the edges little-by-little till it fits.
I did have a couple older AIRE single and double IK foam floors in storage and might be able to send one your way, if you’re interested in going in this direction and repurposing them?
PS a buddy has a double Achilles and I maybe able use his to trace and and get measurements, if yours is a double.