Where are you getting your readings from? Is it from the very bottom under the substrate by probe? The reason I ask is because I have only ever used two hygro/thermo meters at the top of either side of my tank and most times my humidity is reading between 30%-35%, higher during a shed as i mist more often. I have never seen any signs of any respiratory problems at that reading and each shed he goes through is one full piece, like a balled up sock. Thats just relative humidity though. I personally find it easier to go by the clumping substrate rule of thumb. Basically just keep your substrate moist enough that if you squeeze it, its able to hold its shape but not leak a whole bunch of water. Also you could try setting his/her water dish on the warm side of his tank to increase humidity.
You will definitely want more objects such as silk vines/plants, fake stone objects such as pillars or outcrops. If you would like I can try to get a picture of my tank setup for you to see, possibly give you some ideas as to what you can do to change the layout of your tank a bit. I have only had my BP reject a feeding once and that was only because the feeder had gotten some freezer-burn.
The other thing you could try is live food (if you haven't already), it may trigger that feeding response better than the F/T. If you do try this though, NEVER leave your snake unattended with live food as it could result in injury or even death for your snake.