The whole window will have a one foot wide window sill. I will have to show you the place to get a good idea of things. Basil planted in teacups for the kitchen, cheap and pretty teacups planted with fresh herbs on the window sill.
Make a raised bed, but with rubber grip points on the corners top and centre, leaving about raise. Get glass top in table size = raised bed garden table for outdoor. Small succulents or fairy garden? Wheels on feet of table/raised garden bed?