If your DM allows it, Favoured Soul would be a good choice to get access to cleric buffs. Otherwise, about the only real support ability in Origins is the wild sorcerer's Bend Luck. Watch for rolls where the stakes are high and your friends barely miss or your enemies barely hit and nudge them over the top.
Hm, multiclassing looking for twinnable support spells, there aren't too many great ones that aren't on the sorcerer list already. You can dip bard for inspiration dice and Healing Word, maybe use Magical Secrets to grab Elemental Weapon or Armor of Faith.
Another idea is to dip wizard for powerful ritual magic, which provides its own kind of support, some extra spells known to shore up one of sorcerer's big weaknesses, and a nifty trick like Portent or Arcane Ward.
Worth keeping in mind that the other half of support is debuffing. Not a lot you can do if you're already concentrating on buffs, but Blindness/Deafness requires no concentration and cantrips like Frostbite (or Vicious Mockery if you dip bard) can reduce incoming damage.
