I haven’t seen my 7mm wet suit (Mares) stretch-out in 5 years. They just don’t do that.
The sizing seems to be a moving target even with the same manufacturer over different
styles of suits. It’s seems to me that most of these things are cut a bit tight. You might try relying on
customer reviews for online sellers as far as fit goes. Many online retailers offer a perfect fit guaranty
where they might pay for or split the return cost. If you are even a bit of an athletic built you may need to go to a
large or even a XL even though you are otherwise in a standard size shirt or sport coat.
Remember a wet suit keeps you warm by fitting snugly. A very thin layer of water between the neoprene and you skin is warmed by your body heat and the closed cell foam insulates you from the water. So the suit should fit snug while not being to restricting or cutting blood flow.
If it’s just a problem with getting into a normally fitting suit there are a few tricks. A little "water soluble personal lubricant" such a KY Jelly or a generic form around the cuffs will help slip the suit over ankles and wrists. A plastic grocery bag slipped over the hands and feet also work remarkably well. Also try to get as much of your arms and legs into the suit before pulling the cuss over hands and feet. Imagine donning a full body condom. (yeah nobody uses them).
If all else fails you can get an custom fit DUI dry suit for only $3500.00.