Steel lets me sleep.
My Contender from MaleChastityNow takes a few nights when I first switch back to wearing it. But I'm just getting up to pee and going back to bed. No real issue with discomfort. Any ball trap device will challenge your 3-4am erection. After a few days I don't notice any sleep issues at all.
My MouseTrap gave me a weird dream that I had my cock stuck in a wrapping paper tube, and I was prancing around naked in front of my wife. Other than that hilarious dream, I never have any issues sleeping in it.
Allowing an erection at night but guarding my sensitive bits is a good balance.
Conversely I'm now Unlocked after 21 days of denial, mostly in chastity, but I keep having the weirdest dreams involving being naked and walked in on. Last night I pressed my erection against the wall of the shower to hide it from a colleague. And earlier I was squirming away from a masseuse too eager to touch my frenum.
It seems my brain has trained myself to hide myself and not have my erections played with even if in my dreams.
Back on topic- custom steel is the best for slumber.