Even under the present system, it is difficult to justify the Party Whip system in democratic or constitutional terms. As far as can be determined, the Whips have no official constitutional standing, and are indeed given largely imaginary public appointments to justify their salaries and offices and staff. Any system aiming to improve the democratic representation of the electorate should require:
No doubt it will be claimed that this would make government unmanageable. But ultimately, democracy is about the will of the people: if they want a strong government with weak opposition, then they can vote accordingly. But if they want other views to be expressed and taken into account, even if that results in compromise, then so be it. The Party Whip system effectively means that on all important issues there is no need to have MPs at all - the result is already decided on the number of seats won by the governing party (or parties!). That is effective dictatorship.
Interestingly, under PFPTP ProFirst, abstention from voting in the House would be a double-edged weapon as it would indicate to constituents that the MP concerned had no view either way on the issue involved, which is unlikely to be popular. An MP's only job is to carry out the wishes of the voters.