I second the opinion to split up Vatican and Colosseum. Vatican tickets go on sale 60 days prior and sell out in less than an hour. Colosseum tickets go on sale 30 days prior and sell out just as fast. We have used Romeinlimo for transportation every time we visit Rome and they are superb. We will be using them on our visit in September. You didn't say when you will be visiting Rome, so I hope you have at least 60 days to go. Romeinlimo has also arranged a city tour for us before heading to the port, visiting Trevi Fountain, Spanish steps, and other spots. Romeinlimo will arrange for a guide but they do not purchase entrance tickets. I was referred to a business partner who procures tickets. I intend to use her services and not have to fret over missing the sales.