I've had good luck with the Fitzwell brand - I got them from 6pm.com. I'm not sure if other online sites are comparable, but 6pm lets you tailor your boot search for calf width, which was really awesome and helpful. There was no anxiety about whether or not they'd fit when they arrived.
I would suggest waiting until you hit goal to order, unless you already know what your calf measurement is at that weight. You might surprise yourself. I'd wanted boots for years and finally bought them last winter... but now they're too big.
I mean, I can still wear them - and what a 'problem' to have, right? - but I'm a bit sad nonetheless!