What to wear on a first date without overthinking it

Most first date advice is written as though you are being assessed. You are not. You are meeting someone for an hour or two, usually somewhere with chairs, and the job of your clothes is mostly to stop you thinking about your clothes.
Dress for the venue
A walk and a coffee is not a wine bar, and neither is a restaurant with tablecloths. If you do not know where you are going, ask. The difference between those three is the difference between trainers and leather shoes.
Overdressing is the more uncomfortable mistake. Being the only person in a jacket in a pub looks like you tried too hard, and it makes the other person feel underdressed, which is worse.
Wear something you have worn before
This is the part worth following. A new shirt you have not tested is a stiff collar and an unfamiliar fit, and you will spend the evening adjusting it. Something you already know sits right frees up the attention you would rather spend on the conversation.
Get one thing right
A jacket with a decent cut, or shoes that are genuinely clean, does more than a whole new outfit. Pick one thing rather than changing everything.
Deciding faster
If you cannot picture what you own, you end up buying something. Photographing your wardrobe once means you can ask for something casual, see what you already have, and look at it on a figure before you commit.