Netgear N300 Modem suggestions?

I have purchased a Netgear N300 with the hopes to improve the wifi signal in my house. I now however need a modem/adsl filter for our internet because our connection is through the phone line. I would have returned the purchase for a combo package but unfortunately I left it too long to install it.

Does anyone have a suggestion for this conundrum?

You can connect the input port of the router into one of the ports of your old ADSL modem.

I think it's been set up in bridge mode with the old router modem all in one which my ISP provided but the signal hasn't really seen much improvement.

Try using a network analyzer and have a look at which channels are unused in your area. Or you can just go through all 12 of them manually and see on which channel you get the best signal quality.