Artchic, my two pennies:
Rock it.

You seem like the criticism gets on your nerves, but at the same time you seem confident and comfortable in your own skin.
The whole beachwear etiquette thing is nonsense. Even if you did look bad in a swimsuit (which I highly doubt, a lot of us are fine with thicker girls), it's not like you alone is going to bring the aesthetic curve of beach America down.

I recently went on a cruise and there were
a lot of people (particularly older) that weren't exactly making the pool areas a beauty contest. Fact is, most of us are some distance from the ideal, myself included (sorry no six-pack, ladies) and a lot of casting goes into episodes of NCIS: Miami to ensure a "fatty" isn't on the beach... or anyone over 40... or kids... Your mom needs to get out more, perhaps.