Firstly, you cannot do a cycle with no filter. The whole idea of a cycle is cycling the filter to build up a bed of beneficial bacteria to control the
ammonia and nitrites to convert them to nitrates and get rid of them. You will forever be doing manual water changes unless you have a large heavily planted tank that does the job for you.
If you do not want a large filter system in there I would put a small sponge filter in there that will at least allow the cycle process to take place and give the water a little motion to keep the temperature consistent.
As far as the boredom goes, some quality time at mealtime and the aforementioned toys (hamster tubing and ping pong balls) do help but time with the main person in their life is the big plus.
Rose