Which door closer do I need to ensure an internal door at home closes right up shut to stop a cat getting in to the hamsters?

It would be best to go for an overhead door closer with latching action (which controls the last few degrees of the closing, and is the bit you want to be sure is working right).  The lowest price one we do is the Eurospec F2003 at power size 3, which is rather strong for a domestic door, but door closers which have adjustable power settings are more expensive like the Geze TS2000 NVBC (goes down to power 2) or the Geze TS4000 (which goes down to power 1).