I was going to suggest getting the Espers Zona Seeker and Golem from the Jidoor Auction house, but now that you're in the second half of the game, they'll be a bit cheaper. Zona Seeker casts Shell on the party, and Golem will absorb physical attacks for the party until his HP runs out. They're both really useful Espers and I always use their summons for the entire game, so make sure you get them.