Does a window need a sill/stool?

Maybe an ages old question, couldn't find anything conclusive online.

In our kitchen remodel, we replaced the window to the three season porch with a new Pella wood window. On the inside is where the kitchen banquette will go. I want to know if I have to put a sill/stool and apron on the inside, or can i just frame all four sides with trim? The sill/stool will be where there is seating, perhaps sticking out in your back when you are seated. I would like to avoid this.

Thanks for looking.

B