Brickwork + pointing around original window in 1920's house

I have cracked pointing on the upstairs corner of my 1920's house. Being very capable of many building and creative construction I knew repointing was something I can do. As the interior walls were showing signs of damp and cracks I removed the wallpaper. When removing it the plaster came away with it. I realised there were cracks and missing pointing on the brickwork. I removed all the lose rendering which included around the original window frame. There are large gaps halfway up both sides and under the frame. What is the best way to mend the surround of the window to ensure it is firmly supported and draft free. Thanks.