Hi, As long as he is not going somewhere else.
At this point I would measure your food and water intake.
A cat should drink one ml of water per pound an hour.
For example an average 10 pound cat would drink 10 mls of water per hour. So that is 240 mls a day.
See if he is drinking a normal amount.
Then start measuring out his food. The amount to be fed should be on the label of the bag. Average is 1/2 a cup to 1 cup for a 10 pound cat per day. Since he does not get much exercise I would feed him on the low end.
That way you can be sure of his food and water intake amounts and if it is below normal.
If that is all normal then I would not be worried about less coming out unless the stools are abnormally hard, dry, small, or large.
And if the urine amounts are small, excessive, or there is blood then he needs to be seen by a vet.
An average cat has 1-2 bowel movements a day and urinates 2-4 times a day.
Does that help? Do you have any additional questions?