Hi! Glad to hear you're taking the plunge :-)
First things first: not all laxatives have to burn. There are three types and you've covered two of them-- the bulk laxatives and the irritants-- and then there's the kind that draw water into the colon. The most effective I've found for those is Epsom salts. You mix a few teaspoons with about a pint of water and then drink it and wait. The salts keep the water bound instead of allowing the water to be absorbed into your body (and the salts aren't either) so what you get is a pint of water that goes straight through your digestive tract, pushing everything down and out. There's no associated pain, and they're also cheap and safe, by which I mean they're safe for occasional relief of constipation (i.e: you should try to have two natural BMs inbetween each dose or you risk developing a reliance on them). The first downside is that things tend to be more watery, but by the way you describe your fiber regime, that might be a non-issue. The second downside is that Epsom salted water is not tasty at all. Some people add lemon to make it more palatable, but if you start with warm water and you drink it REALLY FAST, you'll trigger the stomach to begin the dumping process and you won't have to suffer through sips.
Hope that helps!