OP honestly - prams are much of a muchness, don’t feel bad! I totally get the feeling of wishing you’d splashed out, but if the pram works well enough for you, does the job, it’s fine. More expensive Prams (like bugaboo) are made with far better materials and components, and last for donkeys years, so they’re worth the investment if you are going to reuse it over multiple children. But that doesn’t apply to all expensive systems by any stretch - so you could have spent out the £1200, and be posting absolutely furious that you spent £1000 more than needed!
I had over 50 prams with my first! I hated our pram with a passion, so bought one second hand, then that didn’t quite suit, so bought something else, that didn’t work for us, and on it went. I always got my money back so was never out of pocket - but over 50 pushchairs and never was one “perfect”. (My Britax smile perhaps came closest). Some of the most expensive prams I had were the worst (silver cross as the main example, but the Cybex Priam was insanely heavy)
I am having baby 2 in a weeks time, and have bought a second hand bugaboo chameleon 3, which I got for £65. It is in mint condition, I’ve cleaned all the covers and serviced the chassis.
I’m don’t expect to use the bugaboo all the time after baby is 6 months. For winter we have a mountain buggy urban jungle (lots of outdoor walks here and we cover miles every day generally as only 1 car) also have a Britax b motion to leave in the car.
You’re absolutely right about the car seat - never ever buy second hand. You’re also right that baby shouldn’t be in the car seat too long, it really should just be for quick trips they go on the pram.
But try not to feel bad. If you really want something else, you can see if you can sell yours on and buy something you like second hand (eBay will give you best price, Facebook for buying!) there are lots of pramaholic groups on Facebook where you can pick up a decent second hand pram. It’s also worth seeing if anyone in your area is open to a swap (just be aware if you’re swapping for a more expensive system, you may need to put cash toward the swap too - be very careful with what you’re buying and fully inspect it etc)
Also if you do choose to sell yours on and buy second hand - only ever buy and sell using PayPal goods and services, only ever ship to the address on the buyers paypal. Don’t allow them to pay G&S then collect (they can claim not received).
RE the car seat, you could look at moving baby in a birth-4 rear facing seat if funds allow. Or your existing seat may fit to a new chassis with adapters as PP have said.