I like the idea of sitting in the sphere's mouth. Also, I think a 6th level ability or Invocation that lets it work like a bag of holding wouldn't be bad at all.
Throne of Teeth
Beginning at 10th level your hungering sphere swells in size and strength. Your Sphere gains the Powerful Build trait and you can now ride in your sphere's mouth, gaps in its teeth allowing your legs to dangle freely and its tongues providing a soft cushion, this uses the normal rules for acting while mounted.