Hi,
To be honest, I would probably just leave a natural divide. What I WOULD do however, is create a curvilinear, sweeping division to mark the different area. Large sweeping curves iswhat I see. I think this would look the most natural. If you planted a few, nice shade trees in the cut lawn area, it should look nice.
You can also add some meadow flower seeds to the natural area!
The area at your house that is 2 feet wide is a challenge, especially if you want some height.
Why not make it all perennials? This would be a lot of fun and add a lot of color. The winter scene would not be too exciting, but maybe that is less important.
Some you might consider is Lavender (tall variety), Daylilys, and Delphinium for height.
You might also consider putting up a few trellises with climbing, flowering vines.
Also I would strongly suggest adding trees at your house corners and also near your front door entry. Your home is long and this will help to frame it.
