Exped is awesome, but OP might save some money by going with a knock off, like Lost Horizon. I've slept on both and didn't notice any meaningful difference in quality.
https://www.amazon.com/LOSTHORIZON-Camping-Mattress-Self-Inflating-Sleeping/dp/B0DSVSXGHG?th=1.
Since you're just planning to car camp, and not backpack, then get a self-inflating foam camping mattress. You can get the Lost Horizon on Amazon in the Single Slim size 62"L x 26"W x 3"T
4 inch inflatable foam mattress, a double works for two people lying basically side by side which means not a lot of room to move. So if you move quite a bit in your sleep you probably want a double + single or even two doubles, but that also means you need a larger tent.
On a budget you’re probably looking at Lost Horizon or Hikenture (both available on Amazon), and likely at the pump sack versions.
If you have time and can wait for a shipment, you can try Mountainhiker on AliExpress, a double with the air pump ranges from $110-130, check different shops for the best price.
Lost Horizon is great for cold camping, they'll stay fully inflated at below freezing, but you do need a pump to deflate it properly, still the most comfortable camp mattress I've laid on
Bank_Gothic
