Bronze CREST project ideas (Fact Sheet)
That website has a whole bunch of ideas for science experiments, and there's a quiz you can take to find one that interests you.
Blue CREST project ideas (Fact Sheet)
I think these ones were more challenging, there was a gold one I think also.
Bye...
I don't know this for sure, but to do two degrees, you would be spending at least eight years of your like in university. You should choose the ones you enjoy most, and would be most beneficial in your future.
I think Physics is meant to be harder than Bio. In the end, though, I guess it comes down to what you want and like, and what you're planning to do when you leave school.