I've done quite a bit of BGs (minimal arena) with 5x SL/SL locks. They have full vindicator and essentially full S1 gear which puts them at 375 resil and 14k HP unbuffed. With that kind of setup, on average, you will find that it takes 4-6 random BGers or 3-4 really well geared and/or coordinated people to do some serious damage to your group. To summarize, SL/SL warlocks in PvP gear are hard to kill. The worst scenario is when you have a few people who graveyard zerg you and keep you in combat preventing you from eating/drinking. You probably wouldn't require super heavy duty direct healing, you just need a healer that complements your team the most and wouldn't die in a couple seconds of hard focusing.

My recommendation would be a priest. Disc for PvP and Holy for PvE. Instants (shield, renew, PoM, CoH) will compliment your dps style of dot and run, and your AOE heals (PoH, CoH) will be an efficient way to heal up your lifetaps which you will most likely be casting simultaneously on your locks. As discipline, you lose some healing and CoH, but gain a lot of utility and become a very hard target to focus down. A fair trade IMO. Paladins need to stop to heal and have no HoTs. Both classes are very rugged healers, but the priest's abilities are too hot to resist. If you still think that priests are too squishy, don't forget all the CC you have at your disposal. Holy priests are the way to go for PvE unless you wan't a class that can tank.