recommendations for a late-18th/early-19th C English men's shirt pattern?

Hello good people, I've been looking into making a men's shirt for myself (yes, inspired by multiple viewings of Master & Commander) and wondering if anyone has any sage advice in terms of self-drafting (i.e. the square cut) vs buying a pattern from Laughing Moon or Black Snail etc.

I did self-draft my chemise and it turned out okay but funnily enough I often find simple patterns made of simple shapes far more bamboozling than more complicated ones!