Seraphicaller is the biggest upgrade you can get, brings your avatars up to ilvl 119, comes from hard mode mission battlefields. But before that the eminent satchet brings them to i115 and is easier to get as it comes from sparks.

Upgrading pieces of AF, relic and empy armour is great from smn due to the smn specific stats and the fact your ilvl doesn't matter as avatar level is dependant only on the satchet. SMN cape from ambuscade is good for avatar level +1 and blood pact damage +.

Getting some job points is another great way to get better. We've got some nice pet options like BP damage +, magic damage, attack, magic acc, acc. So if you can get a CP party that's a good way to improve practically for free.