Yes, probably. I say "probably" because some (many/most?) of the "free" broadband routers bundled with ISP deals have locked-down firmware that won't allow it to be used as a pure router/switch without the ADSL modem bit - you'll just have to try it to see.
Failing that you can easily get a thing called a "broadband range extender" which can be used as a seperate wifi access point. They're intended to be used as "repeaters" that receive a wifi network and "extend" it, but there are some which have a "Wireless Access Point" (WAP) mode which uses an ethernet cable to your main router. This is obviously more useful because you can have completely different wifi settings on the WAP, which could solve your problem.
In its simplest form it could just be one of
these things. That's the cheapest one which is single-band and 300mbs, but they come in a range of speeds and also have dual-band versions depending on what you want to pay...
My house is what's called a "staggered bungalow" (ie it's on the side of a hill and is partly single story, but has a two-storey part as well) which was originally two 200-year-old cottages that were combined and extended under a single roof. The original walls were flint, and this includes some of what are now internal walls. Flint is completely opaque to microwaves, so getting decent wifi coverage for my teenage daughters (who consider wifi a fundamental human right, obviously) presents a challenge. I have used a number of the dual-band versions of the above WAP - one in each of the girls' bedrooms, one in their "den", one in our bedroom and one in the kitchen, all connected to the main router with ethernet cables (run through the loft). They are configured as WAPs rather than repeaters (aka "range extenders") have seperate names and crypto keys, and they are all registered on everyone's phones, laptops, tablets etc. As you walk around the house these devices seemlessly switch to a good signal whenever the one they are currently connected to gets too week. They're inteded to just sit in a mains socket, but a useful tip is to make a short extension lead so they can be sited on a higher shelf (they work much better if they aren'ty at floor level).
€0.03 supplied,
HTH,
PDR