I got this one from boots and it’s nice: Babymel Georgi Eco Convertible Backpack Caramel Leopard https://www.boots.com/babymel-backpack-georgi-caramel-leopard-10336733
I bought a skip hop baby changing bag off vinted as a friend who reviews bags recommended it.
We have a Joules Dinky one (actually 3 now 🙈) which is excellent. It has a sort of shelf bit in the main part and a zip at the bottom so you can easily get to the stuff at the bottom without worrying about the stuff in the top. I would definitely go for a rucksack one personally. I started off with a shoulder bag because I don't wear rucksacks but trying to balance it and get baby in/out of the car/pram/whatever turned out to be a total pain
https://www.smythstoys.com/uk/en-gb/baby/baby-essentials/bathing-changing-and-potty-training/baby-changing-mats-and-bags/qplay-changing-bag-travel-set-grey/p/204659 we got this one from smyths toys online, it came in the post really strong and comes with clips and the extra compartments xx