Hi, ny,
I do not think there are any other OW lounges at LGW North Termnial ( where BA flies from) . AA uses the Terraces.
Id you have a Priority Pass card you could use the Delta Crown Room ( close to the BA Terraces).
I have found the LGW terraces to be very nice ( spread over two levels) - whilst not on a par with the VS CLubhouse ( no hot food or Vtouch salon etc), it does have the usual breakfast selections and sandwiches later on.
It does beat the general lounge area by a long way!

Regards
TBS