You can check out the size of rental models available online. Most of them are manual transmission, so if you are not used to a stick, be sure make a request for an automatic.
BTW—In Rome, after a half dozen visits, the only line I have ever stood in was for the Vatican museums. If you don’t want to stand in line you can get there at 7 AM or for a hefty price there are private night time visits for small groups of ten at a time. Last time I checked around $200 pp.