Have you tried Machs in Fit 1? I hear that Shadows have a different fit, so I can't speak to those.
I've always struggled with heel lock, and the boots that came closest to providing it caused pain elsewhere. I skated Mako/Mako II for many years. They mangled my big toes, but at least they kept my heel in place. Every year, I'd try another retail skate or two, but they either didn't support my foot or crushed my arch or toes. Even True botched customs for me in 2015 and 2021.
This year, I tried Hyperlite 2s Fit 1, but the arch pain was excruciating. On a whim, I bought a pair of demo'ed Machs in Fit 1. I didn't bother baking them before I skated, just put in some Powerfoot inserts I had laying around and the Speedplate 2s from my Makos. Against all odds, they felt great and supported every part of my foot. I'm not going to bake them or even rebake the Speedplates. I've skated in them for maybe 20 hours at this point, and no issues. If I really crank the laces over the arch, it hurts, but I don't need to tie them very tightly.
Hope you can one day find something that works. It's not a fun journey.