Keep the order in which the original Constitution is organized (as well as our federal system), but have it rewritten so we would have a unicameral parliamentary system with
mixed-member proportional representation (with a 5% threshold), incorporating the original ten Bill of Rights amendments including an explicit
right to vote (for some reason we don't have that), an equal rights amendment, and
automatic, universal voter registration. The President (like the Governor-General in British Commonwealth countries) becomes a purely ceremonial position.
As for the judiciary, we should follow the
New Zealand model. The Chief Justice would be appointed by the President on the advice of the Prime Minister, and subsequently voted upon by the full Congress. All other justices and judges (at the federal level) would be appointed by the President upon the advice of the Chief Justice, Attorney General, and Solicitor General, and also voted upon by the full Congress.