What I learned when my niece rented boots (skied 1-2 days a year at most in middle school and high school) is that even when all the rentals skis are the same, there may be different brands of rental boots. So if the first pair of boots feels bad, it's worth going to ask for a different pair. Differences in cuff height made a big difference for her because she's relatively short.
As intermediates skiing groomers, having a boot that's a size too large won't be that noticeable if the ski trip is short enough that you don't develop a bruise somewhere. Have you read the info about shell fit? If you learn how to take a liner out of boot, can do the check on rental boots to see if in fact they are actually too big.
I read about shell fit and I will make sure to do that when I get to the rental store. If I had to guess, I probably need a boot that runs a little more narrow, are there any particular brands to look for? They are coming to our hotel to fit us for our gear so I want to be able to give them as much info as I can to keep the process relatively short.