Definately get a strucural engineer to do a quick, cheap calculation for you on this. You don't want several things to happen: vertical deflection of the joists running onto/into your new beam. this could cause the other edge/end of the joists supporting your bedroom to come off their support, and could cause collapse or "dropping of walls" such that you can no longer open or close doors upstairs. You also don't want to construct your beam such that it twists, if an unbalanced load is coming in from right and left. Lastly, check with your local code official (building code official) who can probably give you a few names of local low-cost engineers to do this simple but inportant calculation for you. Good luck.