You could try a blackhawk in .45 ACP/.45 LC
Single action revolvers have a very natural grip.
Thats the only way to escape the limits created by the dimmensions of the round itself.
The ruger P345 feels very nice in hand too though if you are set on a pistol.
Not that I am plugging ruger.
But thats the cheapest way into a slim .45 unless you go with a norinco and scalled down grips.