Dry Suit recommendations?

Hello.

I'm getting back into diving after a rather long hiatus (14 years). I did my
first dive Sat using rental gear and I'm planning on purchasing a dry suit
since I will be diving primarily in Western Canada and the water here is
dang cold.

I used to own a DUI drysuit shell which I wore with wooley bears underneath.
I sold it about 10 years ago because I didn't plan on doing more diving and
the wrist and neck seals were starting to suffer UV damage.

Looking at the suits out on the market these days there are lots of
different types and I'm wondering if someone can recommend something. Here
is what I see out there.

Shell only. This is similar to what I had before. It requires some kind of
clothing underneath (like wooley bears), is light, easy to transport and
easy to put on.

7mm compressed. This suit is the same thickness as a wetsuit, but is
apparently dry. I know nothing about this type. It seems heavy and I don't
really understand the benefit of having that much neoprene for a dry suit?
Why so thick?

4mm compressed. This is compressed with a different method (or something).
Obviously 4mm is much lighter than the 7mm, but it seems the price goes up
to have less at the same time? Does that make sense to anyone?

With the compressed suits, do you wear a bathing suit underneath and thats
it? is that why they are so thick?

My DUI drysuit shell used to leak slightly around the wrists. I guess that
can be eliminated now by using the sealed gloves.

If a shell suit leaks, your wooley bears get soaked and your cold in the
water. Also if you don't have enough air in the suit and a part of it
compresses against your woolies you will feel the cold. Does this go away
with the compressed suits? I mean, if your wearing just a bathing suit
(assuming that is the idea) and your suit leaks, will you still be warm
while diving?

Has anyone tried all of these types that could comment/recommend one
perhaps? Perhaps there are other types out now that I am not aware of?

I would love to read your opinions.

Thanks.

Doug.