If I had a M-65, my second gun and backup would be a Model 60 .38 snub. NOT a current production item. Get one made before about 1995, when certain changes that we aren't supposed to discuss here took place.
I would not buy a .357 in this model. Other internal changes aside, I think the .357 is too much of a good thing in this size gun.
My second choice would be the Ruger SP-101 with a three-inch barrel. It is probably marginally okay in .357, if you handle recoil well. It's a little beefier and probably more durable than the M-60 if you plan to fire a great many .357 loads. But guns this size are usually fired more often with .38 Special ammo. I prefer the old standard style M-60 snub .38 in a second gun if I had only a M-65 or M-66 or 686 as my primary weapon.
I can tell you, if I had only two handguns, one would be a M-66 with four-inch bbl. and the other, a snub .38 M-60. As you are happy without adjustable sights, your M-65 is an excellent choice. Just don't shoot it a lot with full .357 loads, especially the very hot 125 and lighter weight bullets.
Oh: I would not buy a Model 30 if you have so few guns. If you want a three-inch barrel, look hard for a Model 60 with that length. You'll have stainless, plus a more powerful cartridge and a more versatile gun. I have very limited faith in any .32 Long revolver. For the size and weight, you can carry a .38.