Folks
The recommended approach is to set multiple access points up with the same SSID and same security mechanism and password. You should however assign each adjacent access point with a different channel and ideally one which doesn’t overlap with any others. ie. 1, 6, and 11.
You should then be able to roam and your device should swap from one access point to the other depending upon signal strength. Some wireless cards swap as soon as they detect a stronger signal with the same SSID, some wait until the signal strength becomes unacceptable and then scans for an alternative. Either way the swap between the two should be seamless.
PS. Those powerline thingamajigs work great if you can’t run a cable between the router and the access point.