Small toddler seat?

I’m so lost. Our son (19 months) just outgrew the height requirement in his infant seat, which is what we used for his babysitters for when they need to take him somewhere. I got the Graco Admiral for our car for him, which just fit, and now I need to get a toddler seat for the babysitters. I am considering the Graco Slimfit but we aren’t even sure if that will fit in their back seats. I want him to be rear facing as long as he can and it seems like these convertible car seats are MASSIVE when rear facing. What do people with small cars do for toddler seats? Neither of my babysitters has a small car per se, but also the thought of uninstalling /reinstalling and carrying around a toddler seat to them week after week sounds exhausting. Any suggestions?