I would advise you to look at your stances. If they're greyed out you can throw cards and get seals. You don't necessarily need to throw a Combust at the begining of every fight.
The "only get seals whilst in combat" rule annoyed me so much since i couldn't always tell when i was in combat since sometimes i would throw a heal and somehow i was stil not in combat. It became more bearable once i figured out i could glance at my stances.
