I'm assuming you cannot use a USB adaptor for the cigarette lighter? or does your phone draw more power than the Cig lighter would give it?
I use the below charger if i'm out and about for a long while, it's not the smallest (about the sames size as the phone, but will give plenty of charges (at least 3 full charges) and so i don't need to keep remembering to charge it back up all the time.
https://www.amazon.co.uk/gp/product/B07S829LBX/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
There is a slimmer version of it, with half as much battery power, but will still give a good full charge or two.
https://www.amazon.co.uk/Anker-Ultra-Compact-High-Speed-VoltageBoost-Technology/dp/B07QXV6N1B/ref=sr_1_5?dchild=1&keywords=ANKER+POWER+BANK&qid=1620986311&s=electronics&sr=1-5