I use the fleet composition on the HOI2 wiki,
here.
My navies usually consists of:
-6 BBs (Battleships)
-2 CVLs (Light Carriers)
-10 DDs (Destroyers)
including as many attachments as I can stick on. I've sunk hundreds of ships while losing only one (a Destroyer).
Whatever you do, don't mix battleships with aircraft carriers. Light carriers are fine (they'll provide air cover for the battleships), however. It's all to do with attack range; the attack range of carriers are about 2-3x higher than battleships, so they're basically useless.
A discussion on Carrier fleets can be found
here, but it boils down to:
-6 CVs (Aircraft Carriers)
-2 CVLs
-10 DDs
I only discovered this about a month ago, and since then I've seen a
massive improvement in the quality of my navies. You should too.