In MF 6x12 and 6x17. The roll film holders are reasonable so the chance to try out the format isn't a big reach.
In LF I got a 4x10 back and some film holders. The reducing back for 4x10 was a fraction of what a 11x14 film holder would cost.
All three of the formats I mention work with my lenses. Anything that covers 8x10 obviously works with smaller. 120 film isn't an issue. Cutting 8x10 in half hopefully won't be an issue. New film holders are being made for 4x10. So other then things like film sleeves it's not much effort to shoot. Very painless.
Of course the fact I find 8x10 too square often is the big reason for me.