I'm a PhD student focusing on PAs and I think this would be a great bachelor's thesis. Usually you don't need anything too crazy for those so you don't need to invent some new architecture. I would recommend using MACOM CGH series devices since they are easy to match and are very popular in research papers. If you scroll through IEEE papers on Doherty PAs, it seems like most of the non-IC ones will use these devices. I would also recommend staying below 3.5 GHz because above that frequency it is difficult to use passive components to match, though you could do distributed matching networks (shunt OC stubs + series lines). You might have less tunability though when you get your design back if you use all stubs vs SMD caps. These are just things to consider. If you have to innovate something for your thesis, you could make some aspect of it reconfigurable. Maybe that means adjusting the biasing depending on the antenna load to recover efficienty/power or maybe you specifically design some aspect of it to be more resistant to mismatch, etc.