I've tried on boots but I can't really notice the pain until I start snowboarding with them. I would just like to know a common brand that is known to have good quality.
If you're flat footed you might try investing in a pair of Superfeet insoles. I have a pair of Burton Freestyle boots that feel fine when walking around but when strapped in and riding they hurt A LOT. I loosened my lacing a bit and got a pair of blue Superfeet (I'm really flat footed) and the pain is gone now.
Can you get those blue superfeet insoles at like Walmart or something? Because I have Burton Freestyle boots also and I'm kinda experiencing the same thing you did. It only hurts when I start snowboarding. And I'm really flat footed just like you.