I have used an old wifi router (#2) to act as an Access Point
This is connected to my main router (#1) via a wired ethernet cable.
Router #2 then broadcasts wifi to the local vicinity.
These 2 links will help:
In your case you would also need another old wifi router (#3) to connect to router #1.
Use an Android phone or tablet and install the Wifi Analyzer
On the left hand side there is short video which explains how you can select the best channel and optimise your signal strength.
Don't buy new wifi routers as APs. Recycle old ones from friends, neighbours etc.
With a repeater/extender, the device has to talk in two directions i.e. picking up the original signal and throwing it back out again to your wireless clients, it does mean that the bandwidth is halved
by the time it gets re-transmitted. By the time its done this, your wireless speed will only be half as fast.
There is no loss of original signal strength
using another router as an AP.