I am still in the 1.8 gallon pots I originally planted the seeds in hehe. Never transplanted these babies a single time.
They are now 77 days old, 45 in 12/12. You don't go rootbound in coco very easy, it is possible but you can use less than half size the pots that you can with soil.
However.
You need to water a lot. I never go more than 18 hours and normally 12-14h. So, if you wanna use coco and still want to be able to leave your plants for more than a day now and then you need some sort of feeding system.

Puffzter