I have these and they did the job for me.

TFY Universal Car Side Window Sun Shade - Protects Your Kids from Sun Burn - Double Layer Design - Maximum Protection - Fit Most of Vehicle - 2 Pieces (Regular Contoured Window) https://www.amazon.com/dp/B00Y9SM9M6/ref=cm_sw_r_cp_api_i_ZbkEEb1MRB7AY

I bought the cheapest inflatable twin size air mattress that Walmart sold in stores. It has worked fine for me (5’8”, 150lbs). If you need room for a second person, I think some folks have had luck with the standard size. I also bought the cheapest float/mattress pump they had. https://www.walmart.com/ip/Ozark-Trail-Air-Mattress-Twin-8-75-Blue/285055665

I got some screens on Amazon that also have worked well, but only used a couple times so far. https://www.amazon.com/dp/B00Y9SM9M6?ref=ppx_pop_mob_ap_share

I got a string of LED lights called the Luminoodle ages ago. They run off of any battery bank with a USB out. They can be bunched up and placed in their white pouch to act as a lantern if you don’t want to string them up. I got it when they first came out so it was cheaper then. There might be better options these days, but I’ve been happy with it! https://www.amazon.com/dp/B0198VDWMY/ref=cm_sw_r_cp_api_glt_fabc_Y6WP1DW0059NZT7HBT23

You didn’t ask, but I also bought a portable rechargeable fan for camping in the car. It really helps circulate the air. Amazon doesn’t sell my exact model anymore, but it was very similar to the one below. It can run all night on low. https://www.amazon.com/dp/B01FFWG0I8/ref=cm_sw_r_cp_api_glt_fabc_AW16QGBYD0FD80TC6SZJ

All that being said... I still consider eventually getting the Luno mattress. I just love the perfect fit, finish. Looks nice and I wouldn’t mind having the space to really sprawl out. But for now, and at only $8, the air mattress does what I need.

Edited to add a pic of my set up. Very basic, but cozy. https://i.imgur.com/rSklF0V.jpg