technically it wouldn't boost the signal from the main source, it would create another wireless network at the new source.
If both base stations are configured with the same name, wifi standard, encryption etc then the effect should be that the original wifi network has been extended and devices should be able to transition between either base station at will, without it being noticeable by the user.
I can't recommend anything since I've only ever done it with professional grade devices. In theory just about any wireless router could be (ab)used like this, especially if it runs dd-wrt. make sure the 2nd device supports the same wifi standards and encryption used on the main router, disable DHCP on the 2nd router and set the wireless up exactly the same as the main router, but on a different (ideally non-overlapping, eg 1,6 or 11) channel, then plug one of the LAN ports into your ethernet connection