Buoyancy Shorts - do they help

Probably not as much as some lessons from a swim coach.

sinking legs are symptomatic of someone with either:

weak or ineffective kick
Lifting the head rather than rotating to breathe 

BT has a good TI video that helped me a lot a long time ago.  The key was to establish balance in the water, to raise the legs it has to start up front with dropping the hands, which will lower the shoulders and everything connected to them! The other help with lowering the hands in the water was I could then perform a better catch which helped with the stoke and distance per stroke.  It was a real 'aha' moment for me in swimming. 

You can view and download the TI video here: https://beginnertriathlete.com/cms/uploads/TISolvingSpeed.mp4

For the balance discussion you can forward to ~ 31:40.

I'm about 11 years into AOS (Adult Onset Swimming ).  The #1 improvement for me is getting my legs out of the way.  I have no real propulsion in my kick - it's simply a tool to get my legs out of the water.  I struggled with this concept for years, trying to achieve a "balanced" body position.  Problem with most of us leg sinkers is that when we think we're balanced. we're not even close.  I then learned to "swim downhill" more - head lower, reaching a little lower in the water on the catch, which has then brought up my legs.  They still drag like crazy because I have totally inflexible feet and I get lazy when I fatigue, but it's way better than 10 years ago, or even a couple of years ago where my swimming technique was to overpower the water with my catch/pull.

One day I'll put both concepts together LOL.

Welcome back.  

I had another thought.  Are you wearing swim trunks or jammers?  

if you’re not wearing jammers, the drag from trunks also slows you way down which can contribute (less than head position and kick) to sinking legs.