I feel like most men’s clothing tends to either be very casual (t-shirt and jeans) or very formal (suit/slacks/tie), is there any advice you can give to men trying to find something more in the middle of the spectrum?
I get what you mean, but you’re looking at it in the wrong way my friend!
Jeans are casual, sure. But there are formal jeans and informal jeans. A slim, dark pair of jeans can be far more formal than a pair of dress pants – you’ve just gotta wear them in the right way.
In men’s fashion, think of formality as a gradient. On one end you have the tuxedo and tailcoat – the two most formal men’s outfits. On the other hand, you have nakedness. If a particular item of clothing brings your outfit closer to the tailcoat (which is black, dark, plain, crisp, sleek) then it is formal. If it brings it away from the tailcoat (light, bright, colourful, embellished, complicated) then it is less formal.
There are many, many, many jackets that would suit your needs – look for sport coats and blazers (google the distinction between these two styles) that have lighter colours. Greys, charcoals, patterns – that sort of thing. Doesn’t have to be bold or garish, just things which give the garment more depth and texture. Dark, slim, plain jeans are your friend, as are dress shoes, dark sneakers, work boots and so on.