If you want to stick to the rules, the 5E DMG p.38 indicates for a high level campaign 5th level characters would have 500 gp plus ldlO x 25 gp, one uncommon magic item, normal starting equipment. And, there's a handy pdf on the
wizards' site for Magic Items by Rarity, so finding Uncommon options is a snap.
However, I recommend editing that list as I it difficult respecting a list rating *a* Potion of Hill Giant Strength, a Sentinel Shield, and a weapon of warning as all equivelant to a Weapon +1.
I side with CapnZapp that a +1 Weapon is easier to handle that magic armor, but I think some Adamantine or Mithril armor with a minor property or two from the tables on the DMG p.143 can be much more interesting that unbalanced. Some extra thought might be required to make "Conscientious" as attractive as "Guardian" or "Illusion" however.
For all the things about 5E that I enjoy, the magic items rules are generally such a headache. I'm starting to think going back using the 3rd edition Magic Item Compendium, with doubled magic armor prices, might be a lot easier.