As part of a much larger building project, I will be replacing a 12 foot section of wall between two rooms, which includes removing two 2x4s and one 4x4. The 4x4 is due to the house being built using balloon framing. The wall used to be the exterior wall of the building; as such, it is definitely a load bearing wall, though it is only supporting the roof. There are no floors above.
My question is about support. Everywhere I've looked says that any passageway through a load-bearing wall must be supported by a cement lintel or similar; however, that seems like overkill, since the wall is only going to be holding up a portion of the roof and ceiling.
I am planning on using two sistered 2x10s, supported on each end by vertical 2x4s attached to the original vertical supports (4x4s, in this case). Will that be enough to support the arch and the ceiling/roof above? If not, would adding a third 2x10 help? If those options aren't enough, what other options do I have?
On the other hand, could I safely use less support - sistered 2x8s, or even 2x6s?