Any point to a relatively loose binder?

I've been looking into binding but all the descriptions make it sound like they feel at least as tight as a snug bra, and I can only wear bras that are a size too big in the band or I get nauseous. I can manage tightish stretchy shirts and they squish things down a bit, would a relatively loose binder (eg a size or two too big) be any more effective than a tight shirt or just a waste of money?

On the plus side my dysphoria is relatively mild and only intermittent (I'm genderfluid), so if I can't ever look totally flat I'll be ok. But it's worth a shot :)