Internal wall removal

[mballi]

Hi all,
Looking to remove this internal wall thought it was not load bearing but the single felt flat roof joist is above this the wall is 3 m across a 6.5 meter single story extension

Would a single lintel be fine to support this?

 

[mballi]

Opening will be 1.9 MTRS so assume a standard 2200 lintel would suffice giving 150mm either side
When removing top course of bricks there would be still a full brick and half either side would I still need to prop up during install ,and to get correct height of lintel would I achieve this with some sort of pad to raise lintel to correct height?!