By "traditional size" I assume you mean 1" TT- 1 1/8 DT? There's probably a good reason that really thin wall tubes are hard to come by in these sizes. You didn't really state whether it is the "comfort" of a flexy flyer, or a lighter weight frame you seek. Or is it just the appearance of the smaller tubes? I'm with the others here and suggest larger tubes. Of course it depends on the purpose of this bike.

Personally I prefer a "stiff" frame. As Andy mentioned there's nothing more unnerving than a hard descent on a noodle. There are other ways to build compliance and comfort into a frame rather than resort to small diameter lightweight tubes. If the purpose is a leisurely jaunt on the MUP- do whatever you want.

Building small lightweight frames has it's challenges. I know- I'm one of those short guys and I suppose my frame size is what would traditionally be classified as 48-49cm. You'd think that a smaller frame is lighter. Not necessarily so. It's the tube selection and availability that messes the whole thing up. Generally the thinner wall, larger diameter (lighter weight) tubes don't have adequate butt lengths to be used in smaller frames. So... I accept the fact and live with a few more grams.

If light weight is your goal, get there with component selection. A steel frame is gonna weigh what it's gonna weigh. I have a tough time doing a steel frame in my size at much less than 1500g, unless I sacrifice on what I consider to be good joinery and design. I can do bigger frames lighter than the little ones. At 1500 gram frame weight one can still build a 13# bike.