When it comes time to add a new tort to your family I recommend you ask around for breeders/rescues on TFO so people can help you find a healthy baby who had a good head start in life.
I lost a Leopard tortoise this way a few years back. It is difficult when you really try hard & make the effort to do everything " right ".
There are several breeders on the forum here who really start out babies with the best care possible. To me, it would be well worth it to get one of theirs .. Or on a recommendation from them.
For me , supplementing greens with Mazuri & a variety has proven optimum.
I would recommend ordering one bag of mazuri. I had a similar issue with bogart not gaining weight and it was really scary. As soon as I started him on mazuri he started gaining super fast! I mixed it in his greens and he was eating like a savage beast! Haha it just took one bag and now I have him on basic grass and greens. Also babies can be rather picky with grass. Mine is about 10 months now and he still turns his nose up at grass sometimes. Good luck!!