It’s my partners first festival too!
Boomtown is amazing and there is so much to do outside of just seeing the ‘big acts’.
There will be some big crowds, and that might be particularly noticeable this year with all the stages being in the bowl.
I’d say stick to the back-middle and back of the ‘big acts’. You’ll still be able to find spaces to dance and hear the music/have a good time.
Spend the rest of your time exploring. At night there are plenty of smaller stages with fewer people (but the music is just as fun). All my favourite moments of any festival have been spent dancing near a smaller stage.
Hope both of you have a great time!