2nd Router or access point for wifi extension connected by network cable?

Hello, In our house I have a broadband modem connected to a wifi router which I use to connect (by wifi) to the Internet on our only computer. We now have an office which is out of range of the wifi (30 metres and several stone walls). I have run a rj45 network cable to the office and plugged it into a LAN port on the house wifi router. Could someone tell me what I need to buy to be able to connect to Internet by wifi in the office, preferably without having to do any complicated configuration? For the moment I don't need to do any file sharing over a network, but I may need to in the fairly near future. Do I need a wifi access point or another wifi router (routers are slightly cheaper)? Many thanks for any answers.