Here's the situation...
I have a room 19-feet x 11-feet-5-inches. (There is a partition wall in it, but it doesn't even meet the ceiling.) The joists run 19-feet and are 2x6's (truly old 2x6's and NOT 1.5" x 5.5") spaced at 16-inches.
The room is in the second floor of a three-story brick row house, built around 1900.
Clearly these joists should not be running 19-feet unsupported, so I did some investigation and discovered that there once had been a bearing wall running perpendicular to the joists 7-feet in from one side wall, leaving a 12-foot span on the other side. (See the attached sketch for a visual representation.) I don't know when the wall was removed, but I do know it was more than 10 years ago.
Simply replacing the wall is not an option, since the bearing wall in the same position in the lower unit was also removed. Besides, I don't want to cut up the room again. I have found old work permits that show the joists for my floor were sistered when they gutted the lower unit.
Assuming the walls on either end can transfer the load, is an LVL beam, running in the position of the old wall, an option? If so, how do I know what size LVL I need? (There are two bedrooms above this room.) What about sistering the joists, as was done under my floor? I am looking for a DIY option, not to hire a contractor.