[CMB]

Behaviour is a good way of knowing. Bar chewing particularly is often a sign something is not right in the setup. It could be because the wheel is too small to run on comfortably, or not turning. Hides are too small or not dark enough. The water bottle is stuck and no water is coming out. Some hamsters are more active than other and just need more space for toys and running about.

Before getting a bigger cage you can check other things like those above. See the cages thread to see how much will fit in various cages. This is a good way to help choose a cage.

Tubes, bendy bridges of appropriate size. A box for digging/deep substrate, a variety of things to chew. Things to climb over are good for hamsters.