As Jim indicates, a Virgin Media Hub is usually referred to simply as a wireless router but it actually contains both a modem and a router.
Any other mainstream provider of home broadband services will supply their own wireless router (incorporating a modem), so you'll still have a wireless network throughout your home. Some routers provide better signals than others though, so a router from a different provider might be either a bit better or a bit worse at getting a signal to the upper floor of your home. That shouldn't be any reason to worry though, as the chances are that a different router will work just as well for you anyway. (Even if it didn't, a cheap wi-fi extender, for £13 from Amazon, would solve your problem).
Almost all broadband providers include a free router (or a router on free loan) with their deals but it would best to read their small print to ensure that you're not expected to provide your own. (My own ISP is one that targets business customers, rather than home users, and requires their customers to provide their own routers but such a policy is extremely rare with companies offering services to personal users).