Jeans: Don't wear them constantly. Get decent proper fitting wool pants; plain blue, black, or brown. You instantly look five times better. Also, they're more comfortable.
Shorts: almost never. You're not 9, or trailer trash. Get summer-weight wool/cotton pants and they're about as cool as shorts. Adult men look ridiculous in shorts and it's somewhat rare to see it in most places outside of America.
Synthetics: never. Clothing is made of wool and cotton.
Tailored dress shirts sounds excessive to me. Just favor those marked trim-fit if you're thin, and be careful about the styling; cheaper ones often have outdated over-sized collars.