IMHO, BUTTONS ARE a critical consideration, yet QUITE often over looked.

Here is my take

1. On TWEEDS = LEATHER covered, as McMurdo suggested. ( but I suggest make them removable for dry cleaning purposes )
Antler, Real is great, but a VERY GOOD faux antler, such as the ones Victoria provides (made by the Capt.) are VERY NICE
Wood is also a good type BUT make them "removable" (see below) Dry cleaning will destroy them.

2. On Dressier, such as Crails etc. = Subdued metal, such as Victoria suggested.
Matching cloth covered

NOTE - I advise, if possible, to put your buttons on so they can be removed. This allows you to remove them for dry cleaning & allows you to change your LOOK