ok, so I think what you need is something that has good synergy with your Swellow. If Swellow is your lead, then after you protect to get the burn status, you may need something to switch to if your opponent brings in a counter. counters would usually be scarfed electric or ice using pokemon. common counters would be; latios, starmie, rotom, terrakion, zapdos (you get the point :P)
I would suggest a specially defensive ferrothorn. with twave to cripple the faster threats. what do you think? it would wall most of those counters as well as long as they don't have hp fire.