I tend to substitute specific focus objects for material components, e.g. the classic wand, staff, cauldron, pointy hat, etc. Although any appropriate object can be chosen - if you want to make sure it's difficult to steal, you can pick a massive throne or cauldron.
I'm also experimenting with tiny bonuses; a wand applies a -1 save to foes when it's used to cast evocation magics, and so on.
Further: usually a wizard has to select their chosen item type, and from then on it's permanent - without their staff they cannot cast any spell that needs a Material Component. This allows for some extra personalisation, as well as having (for example) The People Of The Black Circle all use the jawbone of a foe as a focus, by tradition.