I don't think OTL's Versailles could be significantly improved upon, except by some minor changes which may slightly reduce the potential for local disagreements, largely due to hindsight:
Allowing Danzig to decide its fate in a plebiscite, or simply revert to Germany, after a period of 30 years as a free city. This resolves an obvious future point of contention in a very awkward place.
Either the plebiscites in eastern Germany should be done away with altogether, or some clear prior arrangement should be made concerning the division of the plebiscite zones BEFORE the plebiscites actually take place.
Try to avoid permanent League control of any regions, instead adding places like Memel to other states.
While the treaty in its entirety was clearly unenforceable, I believe there was a reasonable chance that future war could have been avoided without any major changes to the borders drawn at Versailles, besides Danzig.
No any treaty would have been feel unfair and denounced by any lunatic because it hurted their nationnal pride. The great depression played a bigger part in the rise of the nazis then the treaty. They needed something to blame everything and the treaty was an obvious choice.
A good point.
The only solution I can think of which might guarantee
constant willingness of a great power to enforce the treaty more completely then IOTL is awarding the whole Rhineland to France. If the French do not believe that Germany can be appeased solely by territorial revision in the east, they will be much more motivated to act.