An eight year old router is almost certainly a type 802.11G. If so, a modern 802.11N (or the up-coming 802.11AC) router will have much better range and throughout. However, given the size of the property, you may still need a wifi extender. I can't be specific because a lot depends upon the layout and construction of the property. All I can suggest is:
a) Make sure you know whether you need a cable, fiber or dsl router (this depends upon the broadband services available in your area).
b) Research the appropriate routers available in your country/area within your price band.
c) If possible, try locating the router in different places in the house, to achieve the best coverage.