Two items in both names sounds fine and I think there would be no harm in including an extra for each of you. That way you'll get your three separate sources so that box is ticked!
You're right though, generally less is more with visa applications.
You're actually supposed to provide 6 items in each name, regardless of how long you have lived together... even if it's only been a few months (so people switching from 6-month fiance visas also have to provide 6 items).
If you don't have 6 items yet, you need to write a letter explaining why you cannot provide all 6, and why you can only include 2 (or 3).
So, if you do have 6 items each (or 6 joint items), then I would include all of them.
The guidance on the FLR(M) application form states:
Six items of correspondence addressed to you and your partner at the same address as evidence that you have been living together since your last grant of leave in this category, or from the date you first started living together up to a maximum of two years. See Note 11.
And at the bottom of Note 11, it states:
Please give an explanation on a separate sheet if you cannot provide six items; if the items are not addressed to both of you; or if they do not cover the period you are relying on.