Our rooms are usually a set up like in the OP. There's dh, me and dd. You said you don't think it would be appropriate for dd to share even if your boyfriend was her Dad.
Dd is 11 and while she's very conscious about her changing body etc, it honestly wasn't a problem on holiday. Plenty of families manage with Dads and their Daughters in set ups like this, sometimes you need to make minor adjustments so that everyone is comfortable, so dh wears pjs instead of being naked like at home. Changing is done in the bathroom, or if I'm in there, dh will go on balcony, or pop to hotel shop until I text him that dd is dressed, or we meet in lobby.
We've been in rooms that have a dividing wall between beds and honestly they didn't give a great extra privacy, paper thins walls, you can literally talk at a low voice and be heard in the other bedroom.
When dd was younger, we'd sneak into the bathroom for a quickie with shower running, she never woke but we would have said I was in shower and dh on toilet.
We haven't bothered the last two years as she would know why we'd sneaked off and while she most likely knows we have sex, I wouldn't want to make her uncomfortable, we never toilet and shower together at home at there's no way she would fall for that excuse now. Dh and I have been together for 17 years though so 2 weeks isn't a long time :)
In a newish relationship I'd be tempted to bring a grandparent etc and book 2 rooms. Or only have one week away and leave dd with someone at home and then have a week as a family either all three of us or adjust dd and me.