Since you're going to revamp your set anyway, and I have a bit more time than I did when I originally posted this suggestion, let me plug my 27-card set for a moment.
Cellar
Chapel
Moat
Great Hall
Masquerade
Shanty Town
Wishing Well
Woodcutter
Bureaucrat
Coppersmith
Gardens
Ironworks
Scout
Spy
Thief
Throne Room
Duke
Festival
Laboratory
Library
Market
Mine
Torturer
Tribute
Upgrade
Harem
Nobles
For Goko, Donald X. split Intrigue into two halves that could be bought separately. The "Peasants and Aristocrats" half contains all the hybrid Victory cards and the cards that combo with them. The "Underlings" half contains most of the cards that give you a choice between effects.
What I've done here is to take the 13 cards in "Peasants and Aristocrats" and pad it out with cards from the Base Set that complement it well. I chose that half because I think it's more new-player friendly. Fewer decisions should make for quicker games and people won't have to wait as long for their turn to come up.
When padding, I avoided cards that were too close to the Intrigue cards already included. You probably don't need Upgrade AND Remodel. You don't need Ironworks AND Workshop. Nor Shanty Town AND Village. I also tried to avoid duds like Chancellor and Feast, although I included Woodcutter for cheap +Buy and to have a terminal Silver. I mostly tried to include cards that have no Intrigue analogue (Throne Room, Cellar, etc.).
For Attacks, I tried to cover the spectrum (discard, junk, trashing, deck inspection). Torturer already has discard and junk. Spy and Thief are the classic Base Set trashing and deck inspection attacks, so they're in. Thief is quite usable in a 3 or 4-player game, especially with beginners. Bureaucrat is there because it interacts great with all the Intrigue Victory cards. Likewise Gardens is there because it's a Base Set pillar and it pushes the Victory combos.