Like the above poster said, Iruka is good, especially if you have his Y+1 second passive (Teaching Instructions). With that and Gaara you can really stack a lot of shields.

Another option is Summer Ino if you have her - she can be both secondary offense and a little bit of healing too. Plus Fire main's Red Lotus passive will buff her alongside Kushina.

If you want a full on healer you can try Summer Sakura, or Cape/Cloak Sakura if you don't have her. But Summer Sakura is nice because she dodges so she's harder to shut down. I wouldn't put her pos 2 though, probably pos 3 behind Kushina and move Fire main to pos 2.

Killer Bee Seven Swords is another one, he'll shield Kushina, Gaara, and himself, let Kushina attack twice (nice, more healing on) and be immune to interruption.

I dunno which ninjas you have out of these but hopefully one of these can work for you.