Jeez, it unsubscribed me from the thread for some reason.
Anyways, you don't need a tablet. You just need to practice, a lot. You already have photoshop right? That's a huge step towards it. I don't even have it, wish I did. But I use gimp. You just need to think of something and transfer it from memory, or from reference on how it'd look when mapped on a sphere.
I use a mouse m8. It may be tricky Af in the beginning, but improvement is promised.