Low-glycemic "thickening" fruits for smoothies

I absolutely LOVE my fruit smoothie in the morning, however I really do better when I eat less sugar. Even my smoothie is too much sugar right now and I have to drink extra caffeine to get through the sleepy feeling (sugar crash?) an hour after I drink it. Today I looked at the ingredients that contained the most sugar: the banana, and the maca powder.

Maca is a great superfood so I really don't want to give that up. It contains a ton of nutrients. However, I'd like to only use half a banana and then substitute a low-sugar fruit to thicken the smoothie with. I've tried avocado before but I really don't like the taste, but maybe it would be okay in smaller amounts?

I'm open to suggestions! Thanks in advance!