Are you going to dive with it or are you just using it for exposure protection while wading? Dry suits are totally sealed with you inside the seal. The farther you go into the water the higher the ambient pressure so the more the water will squeeze the suit's air spaces against your body. Wading chest deep it's noticeable but is not painful nor even uncomfortable. The only way to counter this pressure is by having a way to put air inside the suit without also letting water in. On a diving dry suit there is a valve and a connection that comes from an air supply that allows you to put more air in to neutralize the pressure the deeper you go. There is also an adjustable valve that allows the venting of air as you head towards the surface so you don't pop out of the water like a nuke submarine, which is super dangerous, and also has a manual over ride to exhaust air in case the semi automatic valve fails.
If you are wading and the suit is too tight, you can just reach up on your neck seal and pull it away from you neck to allow air to flow in and it will help neutralize the squeeze problem. It's should be obvious you can't do the same thing under water as you'd get very wet.
Dry suits are either front or rear entry. If you go alone, you can't close the waterproof zipper on a rear entry without help from another person. Since water doesn't get inside the suit, your only protection from the cold, not the wet, is the insulating clothing you have under the suit. Sometimes you might need the insulation of a specially designed type 'underwear' that provides the max protection against cold. That's an additional cost of the total package. If the water is marginally cold and you aren't up to your neck, maybe the layered clothing done by outdoor folks might work. That would be a layer of Smart Wool with a layer or two of polar fleece on top.
It is really nice to go into the water knowing you won't get wet and that you can stay warm. The downside to the diving suit is, at least for me, is it's really not fun to put on. I am not a spring chicken, but the contortion and effort to get it on is almost neutralizing the advantages. I do have a top of the line suit that was custom fitted, but pulling your neck and arms through the seals really takes some effort. The suits not made for diving might be a bit more comfortable as they don't have to fit as snuggly as trapped air inside the suit is a concern for a diver.
Don't buy one online without first going to a sport's shop and trying them on. If there are knowledgeable people where you can try them on, they can save you a lot of grief later on. Jim