I started out with a Sunbeam SGS10701
for the conversion I detail in this thread
for a FC25FB. It's the smallest useful microwave I've found but not sure if it will work in your case. It's an annoying user interface and is under powered but it does the job.
That thread also shows a clever conversion of part of the lounge seating to a microwave/counter. That will allow you to put any microwave you like in it. Not sure if that would be of interest for your 27'.
I'm going to do that conversion and probably use a 950w Panasonic microwave
. That wouldn't fit where you old one was, though.