This is a job for a structural engineer.  He will have to see the job, work out the loading and the span and then design a beam or beams to suit that application.  It sounds like you need a spreader beam of some description over this window.

You cannot rest a steel beam end onto a lintel, it is a point load and lintels are not designed for point loads.


btw, having one beam cut to shape and welded into the spreader means you are not adding to the beam overall height whereas stacking beams and spreaders does add height (hope that makes sense)

'having one beam cut to shape and welded into the spreader' ........................that's a T shaped beam, we use this method a lot.  On site welding costs about £60 in addition to the steel cost.