I'm renovating my basement, which has one double-hung vinyl window (pictured). I want to add one more on the same wall and trying to get a close match. The windows in this house were replaced in 2007 (manufacturer is Vista).

My question is with the frame around the window, which I assume is from the original construction of the house (1991). I see it is on a window sill, with some kind of frame integrated with it. What is that, do I need to buy that in addition to a new window?

I don't want to damage the siding on the outside of the house, so I was planning to buy a replacement window (not new construction).

![enter image description here](https://i.stack.imgur.com/y1SgB.jpg)  

![enter image description here](https://i.stack.imgur.com/mZC0o.jpg)