You can do lunges with your rear leg on a step or bench or chair, make sure to have your knee go down to the floor. Adding the db's can make this exercise pretty tough.
Glute-Ham Raises with your feet under a couch or someone holding your feet is a good idea. Most people bend at the knees, but I think bending at the hips and touching your head to the ground is actually doable.
Those are the two toughest I can think of, of course one-legged squats but for most people they are not easy.
Workout 1, Mondays
3-4 sets of one-legged squats
3 sets of back extensions, lay over some stairs, off a table, your bed, a bench and wedge your feet against something, hold the db's for added resistance
Workout 2, Thursdays
3-4 sets of lunges with your rear leg elevated, each side
3 sets of GHR's
Back extensions also work your butt, which makes your legs stronger. As you get stronger with the lunges, you can load a backpack up with books or whatnot to increase the resistance. If you can't do one-legged squats yet, just do partials.
I really think undulating periodization is a great way to train. That means that you choose a different amount of reps each time you do a workout. Like monday of week one you do sets of 3 rep one-legged squats and the next week you do sets of 5 or 8, etc. This way the resistance and amount of reps is always a little different.