Just got 200mbps fibre, but wireless signal is very poor with new modem, looking for suggestions...

Hi,

I'm a bit of a networking noob, so please bare with me.

I have an ASUS PCE-AC68 wireless adapter which is supposed to be excellent, I was getting a max signal with our old Vodafone ADSL modem, but now with the new Vodafone fibre modem, I am getting one bar on the wireless signal with download speeds heavily fluctuating.

My room is upstairs, and the modem is downstairs in the living room which is 2 rooms away. The fibre modem was installed about 5m further away than the ADSL modem was in the living room.

But I doubt this would make such a big difference though, so I'm guessing its the new modems fault.

My wireless adapter antenna are probably around 15-20m away, with one floor and about 3 walls in the way.

So my question is, what would be the most cost effective option to improve the modem wireless signal output? I'd prefer not to replace the modem if possible. Is there a good router I can connect with ethernet cable to the modem, which I can then connect to?

Is this the best way of doing it?

Any other suggestions are welcome.

Thanks