Advice for trip to Europe in July

So I posted last week looking for some advice for a summer trip to Europe and the consensus was, as seems to be usual on this subreddit, we were trying to do too much. So we dropped eastern Europe out and narrowed down the places we wanted to see and we're looking for advice on another place to go/alternatives to what we have so far. Here's the tentative plan that needs some work. We also have a couple days we can add to the trip as well. The plan is to leave in the end of June and return the end of July

Frankfurt: 8 Nights

Lauterbrunnen: 3 Nights

Riomaggiore: 5 Nights

Rome: 3 Nights

Croatia: 7 Nights

Like I said in the old post, It will be my girlfriend and I on the trip, My girlfriend has never been to Europe. I am originally from Germany and have family in Frankfurt but I haven't been back in 10 years. So far nothing is really set in stone and we're just going off of advice for places to go. We know we want to see Italy, Switzerland, and Croatia, we're not set on any one place there. We heard Zadar was nice and it might be easy to catch a Ferry from Italy to Zadar compared with other cities in Croatia. The 8 nights in Frankfurt is kind of just buffer and we were thinking about adding in one more stop on the trip we just had no idea what might be a good spot. Maybe Paris?

Some Questions

1. Best place to go in Croatia? We heard Dubrovnick was a bit crowded in the summer. Zadar might give us better access to the interior of the country for a day trip or something like that? Maybe some of the Islands would be nice?

2. Does the Italy itinerary look good? We've been warned that Rome isn't all its cracked up to be but we're really into the history and want to see the Colosseum and the Vatican and such. Maybe Florence would be a better alternative?

3. Any other places you would swap out or add?

Thanks for any help!