[efattah]

First of all you can use speed suits like Speedo Fastskin and Orca RS1. However they do trap some air so you need to drench them and move them around to get the air out.

Then you can try Polartec style materials and clones. They also trap air so they need to be drenched and moved to get the air out. I have a full suit that was custom made from polartec. Sadly the suit builder wasn't very good and it doesn't fit that well. It has silver smoothskin on the outside and polartec on the inside.

Then you can try making a wetsuit out of silicone sheets, which offers significant insulation without air bubbles or buoyancy shift. However you need some skill to make it. It is quite heavy on land.

I have also tried using butyl rubber sheets (12"x12") under an existing suit -- extra insulation with no extra buoyancy change.

You can also smear vaseline all over your body, which extends your time in the water to about double or triple than without any suit, but is extremely messy -- it gets everywhere and it is very hard to get rid of.

You can work on cold tolerance and dive without a suit, which also gives the best dive reflex and is my favourite option.

The last option is to use a speed suit or polartec suit, drench & get rid of the air bubbles, and then put sodium acetate heat packs under the suit, which offer huge warmth without buoyancy shift.

A more advanced option is to get incompressible air filled microspheres, and make a stretchy fabric with melted silicone embedded with microspheres. This would offer huge insulation with no buoyancy change.