We have the same floorplan in our Aspen Trail 2710BH and the kids cannot yet haul themselves into the top bunk unaided. Any type of latter would interfere with the bathroom door. After brainstorming for a long time about a ladder solution, I went with something much simpler and installed a single indoor rock climbing handhold on the edge of the wall between the bunks and the dinette. It is at a height about halfway between the bottom and top bunks. I don't have a photo, but see where the red circle is on the attached picture. This single handhold is used as a foothold, the boys grab the edge of the top bunk with both hands for a hand hold while standing on the edge of the lower bunk, then they put their left foot on top of the rock climbing foothold to use as a step, then they can use their left leg and arms to easily pull themselves up into the top bunk. Getting down is the same process in reverse. The small rock climbing handhold doesn't get in the way of anything.
Here is a link to the rock climbing hand/foot hold I purchased. I just needed one so I picked the one with the largest surface for use as a step.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1