There is a multitude of effects that you can use to achieve this setting.
The whammy really works and is very good for pitch shifting, and i know where you're coming from when you say it sounds muddy, It can sound muddy and even glitchy, which is actually a feature that a lot of people like. I dont know what is your style of play when using the whammy, but for example, any chord that you play, tuned in B or E or whatever tuning you prefer, will sound muddy with the whammy IV. Now if you really need to play chords in that octave lower setting, you can go with the whammy V.
The real advantage of using the whammy is that you can go wild and change the setting to 2 up and do a crazy solo.
When not talking about the whammy, you have the POG, which is an amazing pedal, and has the advantage of being able to blend in multiple octaves, like you want a little bit of 1 up mixed with the dry sound and a lot of 1 down... you can do that with the POG, which is good, but versus the whammy, there is no real time pitch change, that might be bad or not for you, depending on your play and what you want to do with the pedal.
My recommendation, and provided that you want to have a mean gritty tone that sounds full in a 2 piece band, you can go with the EHX Micro synth, which is much like a POG but with some added effects, like the square wave, to get a fuzzy distorted almost-8bit-like tone which depending on your needs can be interesting.
Like these, there are millions of pitch shifters out there that can do what you are seeking. Most are better for this than the whammy because 1st you have a mix control and 2nd because of the improved tracking on polyphonic sounds (e.g. chords), but you will lose the ability to change the effect in real time and there is no dry output (as far as i know, correct me if i'm wrong)
In the end of the day, it's really about what you want to do with the pedal. Now that you know what the pedals can do, you need to have a good idea of what you can do with them, and for that, there's no better way to learn this than testing the gear, like has been said, hit the road and find a shop or a couple of shops if you can't find one with all the effects, and just try them out for a while to better understand your needs.
One last note, ask the guys on the shop. They will have biased opinions most of the times to sell you their stuff, but if you follow my golden rule you will not have any problems:
Never buy the first you try