I discovered I actually like camping (ish) 6 years ago now, for my 40th as well! I previously hated it.
I suggest a decent sleeping bag. I replaced my old one with “The Beast” pod from Millets - omg it’s amazing. It’s huge and warm and I love it.
Take extra layers for the night, especially if you don’t get the above sleeping bag, it gets really, really cold. Socks and jumpers definitely recommended. Put an extra blanket in, even if you leave it in the car and decide you don’t need it.
Camping toilet. I currently get up every 1-2 hours in the night to go (really should book to see a dr to get this checked but anyway) - when it’s freezing and I’m tired, I don’t want to traipse across a field. I bought commode liners, absorbent pads and the stuff that you sprinkle on urine to turn it to a gel. In the morning, take the bag out and refresh the set up for the next night. It was a game changer. Of course if you are only going as a one off you could just buy some portable toilet bags or similar!
Lights. Several ideally! The little d clips are great for helping you to hang these.
A battery powered air pump for your inflatable mattress (recommend one of those too).
Disposable bbq’s if it’s a one off trip.
A comfy camping chair - I have one with an insulated pocket one side and a cup holder the other. High back.
If planning to eat at the tent, some sort of table.
Have fun!