If your gonna bench, you have to pull. Your pushing horizontally, so pull horizontally. You've got a low cable it sounds, so you should be able to set up some sort of seated cable row. Get something to brace your feet to, and just pull the bar to your chest. (you can pull to your lower abs, or neck for variation). 2nd, you're doing military press, so you've got to pull from the top. Your lat pull down, that will, but it is no where near as effective as a chin up. Find yourself a chin up bar, or a ledge in your house where you can do chin ups (palms facing you) and pull ups (palms away from you). You wont like them, it's because they're hard, and very good for you.
If you look at all those upper body exercises closely, you'll notice that they are all multi-joint exercises. It is even more important that all your lower body exercises are multi-joint or total body lifts. Leg extensions, leg curles are not going to cut it. Body weight squats are a start. Overhead squats, (hold a broom stick at the ends, squat down deep - past parallel) would be next. Single leg squats are great, any variation of a lunge are also very good. Unfortunately, unless you can invest in some dumbells, you wont have the resistance for lunges, and single leg squats are very advanced.
You can however, progress with single leg box squats - set up a 'box' (table, chair, whatever) that is somewhere close to 20-22" off the floor. Lift one leg infront of you, slowly lower yourself down to the box, under control. When you touch the box, pause for a split second, keeping the opposite leg in the air, abs/back tight, and drive through the heel of your working foot to stand back up. If you can't control that range of motion, make the box higher. If it's too easy, lower it. You will want to progress until you can do 8-12 reps per leg, in a full range of motion (to a 10-12" box)