this is a different solution, but people recommend these insoles for Rothys, which have a low/minimal profile. I always need arch support and it's so much less stressful for me to shop knowing I can add them in if necessary!
You could but there are plenty of insoles that only go about halfway up the footbed, e.g. these.
I have boots from almost every brand available, and I have flat feet. I have to use arch supports in all of them except for those by Beckett Simonon. They provide great support straight from the factory. Chippewa is a close second, but not quite good enough to dispense with the arch supports.
In a few pairs of my boots I've replaced the standard insoles with full length arch supporting insoles from various manufacturers, but in the majority I use 3/4 length Powerstep insoles. They provide great support but don't take up any room in the toe box.
I have used custom orthotics in the past, but I haven't had any issues with foot pain since switching to these off-the-shelf supports. And by the way, I don't have a pair of these for every pair of boots that I own. I only have a few pairs that get placed into whatever boots I'm wearing.