If you don't know where to start with sailing gear, this is what I use (in addition to items I would have owned anyway like shirts, shorts, sunglasses, sun hat, warm hat.)
It's not necessarily the best, just an example. I spent around £515, but could have spent less for fewer options or fewer seasons.
"Fingertipless" gloves to avoid rope-burn while still being able to tie knots. I've owned both:
lighter-weight Henri Lloyd Deck Grip Finger Gloves (£15 from force4.co.uk) and
slightly warmer Musto Performance Long Finger Gloves (£25 from Marine Super Store) but you don't need both!
Gul Power Wetsuit Shoes (£23) from Watersports Warehouse.
Gul Code Zero Wetsuit Trousers (£75) Mine are 3mm thick, I would recommend thinner for warm weather.
Wetsuit shoes (see above)
Chilly Weather (which for me is about 12° C if not raining)
Full-body wetsuit (perhaps £70) from Decathlon
Tribord watertight ankle boots (£45) from Decathlon.
Gill NeoSkin thermal 'wetsuit socks' (£22) from Wetsuit Outlet because your watertight boots may well fill with water at some point.
Crewsaver Atacama Drysuit (£266) from Wetsuit Outlet. This model comes a removeable fleece 'onesie' to wear inside it.
Normal warm clothes under the drysuit. But avoid hoods and collars!
Boots and thermal socks (see above)
Tip: Label your gear in a way that's resistant to wearing off. In some cases, I cut an identifying pattern into the label, as it's guaranteed not to wash/wear away.