Just an example of a round mirror -- of course -- the exact size and shape really depends on the size of the buffet AND the decor in the rest of the room ....

Also -- if you wanted to add visual height -- then a tall rectanglar mirror would work -- along with a pair of sconces and/or additional small artworks on each side (again -- JUST examples ...)

And -- of course -- adding a lamp OR a pair of lamps on the buffet could change the choice of mirror too ....

Here is a link that might be useful: bellacor -- plain round mirror

Here's an example of a buffet (and mirror) -- there are more on designer Phoebe Howard's website -- might have some ideas there ....

Here is a link that might be useful: example of buffet

Thanks teacats; love the rectangular mirror! Will look for something in that direction. Wasn't sure if buffet lamps were still "in".

I bought the most beautiful mirror from Hudson River Inlay for over my sideboard.

hi gracie01 - what a great buffet to refurbish and use. a dining room by suzanne kasher immediately came to mind when i saw it - she loves to mix vintage with more modern pieces and it could work for you. no "buffet" lamps used here...just a pop of color from the vases. simple and elegant.
what do you think?

Here is a link that might be useful: Suzanne Kasler Dining Room Inspiration