So much Dick, so little time.
Ubik and Three Stigmata are definitely essential so you're on the right track, as is his Hugo-winning Man In The High Castle. If you've already seen the film of A Scanner Darkly I wouldn't make the book a priority, but it's one of my personal favorites and what Dick himself thought was his best.
Others I'd put near the top of the list, that all deal with the elements you're looking for at the moment:
Flow My Tears, The Policeman Said
Now Wait For Last Year
Time Out Of Joint
We Can Build You
Martian Time-Slip
And of course, the VALIS trilogy is pretty essential to fully understanding the mind and worldview of the author. Valis itself is mind-blowing, The Divine Invasion less-so, but the conclusion (and his last completed novel), The Transmigration Of Timothy Archer, is one of his least sci-fi efforts yet one of the most thought-provoking and moving.