You should only have 1 modem because you only have 1 primary communications feed to your house. That feed is a terminal outside your house. You could pay for another feed or split the feed, but I don't think that's what you want to do.
The modem acts as a synchronizer between the network of your service provider and your home network. The 2 networks have different speeds and protocols so the modem modulates/demodulates, speeds-up/speeds-down, converts/de-converts your communications signals.
In addition to being a synchronizer, modems can also include other functions, such as a telephone modem and a home router. Whether you have an all-in-one modem or standalone modem, the router connected to the modem is your Main router.
I think you meant another router...not another modem (or another all-in-one device). Yes, you can add another router in your house. That'd be a Secondary router.
The question is: how would you connect the Secondary to the Main router? You could connect with a wire or with radio signals. Can you run a wire from your bedroom to the Main router? If you could run a wire, you wouldn't need the router because you could just connect your laptop to the wire.
If no wire, then you'd have to connect wirelessly. Ensuring a strong signal is another story. If that's how you want to go, let us know.