Coffee Appreciation

Freshly ground beans will make a whole amount of difference and last longer than pre ground. Also, beans from a coffee shop will be fresher than those from a supermarket (which could have been on the shelf for months). Maybe a porlex hand grinder to keep costs down if you are only drinking a cup a day?

Getting a hand grinder and using good beans is probably the biggest jump in quality you can get. If you’re just drinking one cup a day, a bag of beans for £10 works out to about 60p a cup, and you can honestly make coffee that you’d pay £3 for in a good cafe. As long as you’re weighing and timing.
Edit: didn’t mean to paraphrase @jdp there.

get a set of scales, hand driven grinder and fresh beans.
weigh the beans for consistency/ fine tuning.

I used to use 13.5g beans for an aeropress, inverted method.

Changing from ground to beans will be noticeable, then supermarket to fresh roasted another noticeable change.

Bean region also affect things.
My wife and I prefer South American, I like Indonesian too, neither of us like African coffee.

What's my best next move to up the quality without spending a ton of money ? Is a cheap grinder + posh supermarket beans likely to be worth it or if i'm grinding do I need to get better beans pact/bourbon etc ?

Cheap grinder + posh supermarket beans won’t net you much imo. Your next move up is to get coffee from a roaster and get them to grind it. Next step up after that is to move to beans (which won’t lose their flavour as quickly as ground) and grind with something like a Porlex Mini.