If you want seamless roaming between two APs, then install two *identical* APs, and configure them identically with WDS.
I was with you until you said WDS. You don't need WDS to accomplish the seamless roaming, that's just if you don't have a way of getting internet into the second location over ethernet. Nobody should use WDS if they can avoid it

But if you have an Android based smartphone/tablet with WiFi, then use the "Wifi Analyzer" app instead -- very handy that.
Seconded. I use that app all the time for checking signal strengths on my clients' networks.