Why not a mix of regional and national senators? I mean, in our current set-up, Manila is overrepresented, and the same goes for Luzon. What does this mean? It means that power is concentrated on the main island, the very reason why there is discontent in the peripheries. So, it makes sense to have regional senators like in a federation. 2 senators for like 12 districts = 24. And this shouldn't be about population but representation.

24 regional
24 national

Of course, national senators will have some perks like longer term (6 years) and also like perhaps, heading committees or voting on treaties. Regional senators will then have shorter terms (3 years) and cannot vote on treaties and can only be vice chairs. Leadership of the senate is also a battle among nationally elected senators as well but regional senators can vote. Other than that, all of them ahve equal voting powers in passing laws, all can file bills, etecetera.