unless this kind of thing can be done then there is no chance of a level playing field and there is no chance of policy reflecting the make up of the country for the next fifty, hundred years....
just to clear that up, bc the sentiment about achieving a level playing field is true but some of the details aren't
the biggest problem is the Senate. it's not that "boundaries are drawn unfairly" (that's the House) - the Senate doesn't have boundaries. it's the way Senators are apportioned - equal representation for every state regardless of pop size - combines with current demographics - a bunch of Western states with tiny, rural, overwhelmingly white populations - to give the modern Republican party a huge built-in advantage. you can't change the way Senators are apportioned without amending the Constitution, which definitely isn't going to happen, so the only answers are 1) wait for demographics to turn more states blue, or at least purple, which might take a decade and isn't guaranteed, or 2) add more blue-leaning states - which doesn't require a constitutional amendment, just a joint resolution passed by simple majority - specifically D.C. and Puerto Rico (which just voted yes, albeit narrowly, on a statehood referendum). the Republicans know all of that full well, so without a Democratic majority in the Senate it will likely never happen.
the Electoral College is less glaringly "unfair" - its main issue isn't that it doesn't represent state populations, it's that it doesn't reflect the national population. there are issues with how it represents state populations but they're tactical, like gerrymandering, rather than built into the Constitution. it's based on the census, which is why the Republicans devote so much effort to sabotaging the census and trying to turn it in their favor - i.e. trying to ban modeling in favor of traditional door-to-door methods (which always undercount minorities, the poor, etc), adding unconstitutional citizenship questions, etc - but even assuming a relatively accurate census the structural problem for the Democrats would be that they run up the popular vote winning big in big states which doesn't help them more than winning those states 50.1-49.9 would. the only way to change that would be, again, constitutional amendment, which isn't going to happen any time in the foreseeable future.
the number of Supreme Court justices is
not determined by the Constitution, and could simply be changed by Congress, with justification. there would indeed be a great deal of howling, and it would require Democratic unaninimity in the Senate and near unanimity in the House - i.e. for Democrats from purple or even red states/districts to bite the bullet - which I'm not sure would be forthcoming, but it would at least be possible with a Democratic trifecta. keep in mind a liberal SC wouldn't be able to do anything about the unfairness of the Senate or EC - it rules on what's constitutional but it can't change the Constitution. tho there are many other reasons to want a liberal SC of course.