well, if Raven wear(of alberta canada) was still in business , they would be my first suggestion, they used to custom make/fit things and about as warm a stuff as possible to own!, the very warmest and quietiest gear I own, sat many minus 20 days from before sun rise to after dark in it and stayed warm on all day sits in Alberta and like COLD places!
wasn't cheap, but Darn it was good stuff
But they closed when Sue retired!
Sleeping Indian makes good stuff too, all depends on what your willing to spend!
https://www.sleepingindianusa.com/
I own both cabela's MT050, there wooltmate series parks(and bibs and even coveralls, and a few other things pants and a few other brands gear, spent a small fortune on things over the yrs LOL)
and they don;t come close to what Raven wear
I think there wooltimate srtuff was warmer than there MT050 stuff, but a heavier bulkier to wear
Over the yrs I also tried them body socks deals, wearing lighter gear and then sitting on one of them, like the heater body suit, worked pretty well, for all day sits in very cold weather, and can pack in pretty easy too!
so might be worth looking into!
https://heaterbodysuit.com/
also you can still find some things for sale on Ebay from Raven wear!