Might look a bit scary but this could be a good starting point, just control the depth
https://www.lovehoney.co.uk/bondage/cock-ball-toys/urethral-sounds/p/penis-plug-double-ended-stainless-steel-ribbed-urethral-dilator-6mm/a33430g59508.html
Oh and my wife really quite enjoys a sound rod in her too,
Also see this thread Urethral Sounds - #31 by randystevens1950