I know you said you don't want to change the housing, but I don't think I'd recommend just buying bulbs. The reflectors are what's horrible on these headlamps. Even the stock lamps put out a decent amount of light, it's just that it's unfocused so you get a lot of glare. If you put in a brighter light source you just get more glare.
I've got JW speaker headlamps now, but previous Jeeps I put in Cibie E Code housings with Osram bulbs, which are similar to the Hella h4s.
Chris has a decent write up somewhere on different headlights that you might want to review. Really, can't stress ditching the stock housings enough. Skimp somewhere else.