Some random thoughts:
Food, wear and tear on saddles -- exotic animals require exotic saddles and food - so some costs there. Chance of gear breaking if you fall the mount off a cliff or something similar.
Ground terrain differences slow or speed up the mount - some mounts travel faster on rougher terrain than others.
Hedge maze races.
Hazards can be swimming across the river or jumping from stepping stone to stepping stone
Delicate goods being carried such as eggs -- too fast and the eggs break
Dressage competitions - slightly more complicated but can spend money on rider gears
Novelty costumes for animals for halloweed christmas etc if you use a date function
Carts, carriages etc for increased carrying capacity but cost money to hire or buy
Special reward foods used to help train mounts i.e. apples, carrots - these can also be quest rewards i.e. a barrel of apples for helping the farmer moves his crop etc thus avoiding too much gold buildup.
Hiring riders to exercise mounts for you if you don't have enough time.
buying Jumps barrels etc for a competition practice field.
Hope these help
but mostly I hope your health gets better
And wish I could give you more than +1 for perservering through adversity!