Another option for the OP if buying hand built wheels is 14/13g single butted spokes for the right flange and 14/15/14 or 14/16/14 butted spokes for the left. This will allow more balanced tension in the dished wheel while putting more material to the task.
Tension ratio between the two sides isn't going to change with spoke diameter on one side.
Thinner spokes on the left may be good because they stretch more at a given tension so it takes more rim movement (vertically or laterally) until they go slack and allow the nipples to unscrew or wheel to collapse and windup at their low tension is less.
To get more balanced tension you need to change the bracing angle (most probably by using an offset rim (Velocity, IRD), although heads-in radial and cross-1 drive side lacing will do it (with neither being a good idea in this case)) or use fewer non-drive side spokes (triplet lacing between a 32 hole hub and 24 hole rim with 16 drive side spokes but only 8 non-drive-side would do it).