Awesome work with the bench and incline DB PRs. Your strength is definitely on the move. You probably won't plateau for some time, bro. Just keep doing whatever you are doing until it stops producing results. For the side bends, try this: setup the squat rack with an empty bar, load one side of the bar with about 20 lbs (8-10 kgs), double up the collars just to be safe, take the weight out like you would a squat (I use high bar setup for this exercise), step out and begin bending towards the side that the weight is on and then back to start position. I do about 10 reps per side and what's cool about this exercise (or misery inducing rather) is that it works all layers of your core (I think there are about 3) while really targeting the obliques, which are weak in most people. You will feel like you just got done puking when you finish a few sets. You can sift through my log and find some photos in the past few weeks of me doing them. I warn you that they are hard and it does not take much weight. Be ready for it when you take the bar out, as you'll feel your core go nuts almost immediately. Try not to use your arms to push or pull on the bar, just try and hold the bar still as you bend. Also only bend as far as you are comfortable as you don't need a slipped disc or torn abdomen to achieve results with this exercise.