The best action type I can think of in terms of sleekness and trimness would be the "strengthened 46"-type Husqvarna. I have one, a Model 640 in 8x57. It is a commercial action with no thumbcut. Other actions like the Husky 1900 exist and would make fine light carbines also. Think of the later Husqvarna actions {1900 etc} as ultra refinements of the original small-ring Model 96 military Mauser action and you will be on the right track.

The "strengthened 46" is a relatively rare and unique Husqvarna action that is essentially a 96 action without the thumbcut. Mine still has a stripper clip notch. With a trim bolt handle as you envision, it sounds like a winner to me. I do believe you can find one through Allan's Armory or maybe Simpson's if you like it. Both the 46 and strengthened 46 are small-ring two-lug actions {no 3rd safety lug}.

Let's see if I can post these pix:

Here is the top view of a strengthened 46:

Here are three Husky's:

Top: 5 1/2 lb M46 9.3x57 {commercial 96-type action, built 1942} with original HVA peep sight.

Center: Strengthened M46 8x57 {built 1946}. Note sleek unbroken lines of the action.

Bottom: M146 9.3x57 {built 1940}.

All stocks have been modified for left hand shooting. Both 9.3's sported stocks with knife-edge, sharp combs and alot of castoff and I modified them to allow comfortable left shoulder shooting. The 640 {strengthened 46} I did so and left a bit of hog's back in it.

For a super-light carbine, an original HVA peep rear sight would make perfect sense. Here's one:

By all means, document the progress of your project here so we can see it!