Just talking what you asked for (more power on body shots)

For someone in the opposite stance to you ;You can about face and get off a rib shot under a jab that you have just avoided. You stay in your front stance as you turn away your rear glove comes up to the side/back of your head as the other glove goes in hard under the jab.
Its followed by another hook but up high. Its a one two move and you slide in on the second hook with turn.
Takes practice but well worth while.
You can do it in same stance too but you have to pull your front foot around to the rear so you switch as the jab comes in,then it works for that situation too.

To gain more power on kidney area and side body shots; (seeing your out to the side slightly when the opening presents itself) you can turn your rear foot outwards away from your other foot, slide the heel in and it twists your hips and body weight fully into the blow; if you step backwards and slightly out on an angle first it actually takes you away from their rear arm threat as you go.
the arm you attack under isnt a threat if its already expended and you have made contact.

That works best when they are in the oppostite stance to you or when you are both fighting square.
It works well in same stance too ,but you have to be more aware of their rear arm as its closer.

Double hooks ,low then high should be practiced as those openings occur on their reactions to the first hit.

Works high / low too.
To triple up even works.