4G modem only

[BuTTuS]

I've been asked to setup a wifi and ethernet 4G internet connection that basically should be accessible only from within one single room. So I'm thinking 4G modem connected to some wifi router where transmit power can be decreased to almost nothing, would that work?

So I need suggestions on either a

4G modem only, with an ethernet port
or
4G router with ethernet port and the option to turn wifi off and put it in bridge mode
or
4G router with ethernet ports and the ability to lower transmit power

For the two first options I would be using an ASUS N66U with Merlin firmware as router, as I've seen the option to change power there.

Any thoughts and suggestions?

Thanks