My main issue with most classical music is that they feel too heavy and I feel physically sick.
Minimalist: Steve Reich, Henryk Gorecki, John Adams...
But it sounds more like you're asking for classical music that isn't overwhelming. In that case, go for chamber music - this is for any small ensemble. You might particularly like things like Mozart wind ensembles (quartets, quintets), Faure or Ravel trios or quartets (sometimes with piano), etc. There are a lot of Mozart cds "for children" that are good here too, since young children like smaller ensembles better than big orchestras.
However I find it very difficult not to listen intently to Bach. And I mean that in a good way, but disqualifies his work from being my "working background" music. My pick for programming music is the complete Mozart symphonies. They're also works of genius, but I can be in their presence without my mind being constantly drawn to them and away .
I also go for the Renaissance lute works of John Dowland. In many ways the pop music of the day (and noticeably less sophisticated than the baroque that immediately followed) this somehow puts me in the right mood for UI design.
Perhaps "serious" is the wrong term; maybe "methodical" or "mathematically inclined" is better.
Or how about Steve Reich's Music For 18 Musicians? That could be too much, or it could be just right, depending on what about the music makes you feel sick.
I also like LaMonte Young and Terry Riley, but they might be too spacious if you're looking for compelling melody.
Oh, and stay away from John Adams. (Other people reading this looking for heavy minimalist music: go for John Adams. Start with Short Ride In A Fast Machine, and then dig in to the operas.)