Glycolic acid is great for dull skin.
I recommend a glycolic acid toner to smooth and brighten your skin. I've currently got these 3 on the go:
https://www.boots.com/loreal-paris-5-percent-glycolic-acid-peeling-toner-180ml-10305493
https://www.boots.com/Nip-and-fab-Glycolic-Fix-Liquid-Glow-6-percent-10237543
https://www.boots.com/byoma-brightening-toner-150ml-10322984
My favourite is the L'Oréal. Says peeling, but your skin doesn't actually peel. They also have a face wash which is nice.
https://www.boots.com/loreal-paris-revitalift-resurfacing-serum-in-cleanser-150ml-10345748
Pixi is rated well and recommended by loads of people although I haven't tried it.
https://www.boots.com/pixi-glow-tonic-250ml-10256343
I also recommend this mask for use once or twice a week. Been using for years. Really gives you a great glow. It stings and feels a bit itchy when you put it on (like an acid treatment in a salon would), but don't let that put you off or think something is wrong (unless you're known to have sensitivity with certain products!) I find fanning myself helps!
https://www.boots.com/the-ordinary-aha-30-bha-2-peeling-solution-10267772
In my opinion, you don't need to spend a fortune on skincare. The ordinary are really great, with plenty of acids and products to choose from. If you go to their own website, it can give you recommendations for products and regimes for your particular skin concerns and skin type. It's all reasonably priced, so if you decide its not for you then you've not wasted too much money.
Although I'm 41 and starting to get fine lines, my main concern atm is pigmentation, so am buying products to brighten and lighten my skin. Unfortunately I don't have recommendations specifically for fine lines. But I hear haemorrhoid cream is good for eye bags 🤷♀️ and I enjoy using L'Oréal serums and moisturisers (not the cheap basic range).
SPF is a must! Every day, even in winter. Take it from someone with pigmentation issues! The sun ages you considerably, and if you're going to start using acids, you must absolutely 100% of the time use a good SPF30+, preferably 50.
A regime is based on cleanse, tone, treat and moisturise so would recommend all 4 steps, twice a day. Night creams can be quite thick, heavy and greasy, so if you have oily skin, find one for that skin type that also includes what issue you'd like to treat.
Skincare is a minefield!