I have a topline aluminum ladder to access my bunk and it's adjustable by cutting off some of it's length to fit what you want to do. Willett (Northstar) also offers a bunk ladder on their website.
Bought the Topline on Amazon last year. It works very well and is very stowable.
2015 Backpack SS1500
1997 Ford 7.3 OBS 4x4 CC LB