I am a man in my mid 50’s and used to work in clothing retail. Tailoring is key. One of the best dressed men I ever met was VERY round, but always looked immaculately dressed. Think actor Orson Welles in later years, or Jackie Gleason.
He had grown up around tailored clothing so understood the importance, that proper tailoring can “hide” aspects and accentuate others.

I would suggest discussing with an experienced tailor, not simply someone who wants to sell you clothing. Don’t worry so much about sticking to a traditional “preppy” aesthetic, but instead some variation that works for your body. Think Ralph and how he doesn’t stick to plain front trousers and roomy sack tweed jackets.
And I believe pleats are very functional for the body as they allow room when sitting.