For your mtl vaping style you will be happy in the Kayfun range. Svoemesto is coming out with the new Kayfun Prime (not yet released) that everyone is talking about, very soon. (No need for a mtl reducer with this one) Other than that I don't think there are any new mtl rta's out that I know of.
If you want a cheap cheap terribly easy mtl tank there is the
$8.54 Nectar Styled Genesis RTA Rebuildable Tank Atomizer - stainless steel + POM / 22mm diameter at FastTech - Worldwide Free Shipping but I do find it leaks if you lay it on its side, at least for me. Some people have managed to wick it without getting leaks even upside down, but I'm not one of them.. but you can certainly drop it all over the place.
The serpent mini is a definite no for you.
I love my Kayfun four more than anything, but I'm not sure they are still being manufactured. (If you can pick one up you will definitely like it) but the Kayfun 5 overtook the 4 I think. If you look into the 5 you will need a reducer. May as well wait for the prime to come out or look into the mini v3, which is definitely your style of vape, and skip looking at the 5 altogether.
There is the Taifun GT 2, which is more of a mtl than the taifun gt three, very nice vape that is.
I'm having a brain fart right now because I can't think of any others and I have a box full.. lol. I'll add more as I think of them.