I should really be wearing prescription orthotics (arch support and pronation control), but I have so many pairs of boots in play that I'd have to take out a second mortgage to outfit them all.

IME, most over-the-counter orthotics/foot cushions turn to mush in about five seconds.

Spenco used to make neoprene and plastic footbeds with real arch support, but I can't find them anymore.

If you're hardcore, you can make your own by double-layering the wool felt footbeds from hardware and workware stores. They will squish down at the pressure points as you wear them. You'll have warm feet, though (great in winter, not so much in summer).

My current favourite: I've been having really good results with Softec Ultra Foodbeds. You can heat and mold them, but I find I can wear them "straight from the package" and they break in by themselves. Excellent, springy arch support. I get them from Mark's Work Wearhouse (Canadian chain) for $40 per pair. Looks like they're available online too.

https://secure.yoursole.com/ca/footbeds/softec-ultra/