You know what I've always wondered?

[Clueless Morgan]

Hmmm.... Polyjuice potion.... I remember it going a bit wrong... with some cat hair in the mix, IIRC...
But an animagus, like Prof McGonagall, can do it with a wave of the wand.

But there are several more examples of polyjuice potion being used in the books where nothing goes wrong - Harry and Ron into Crabbe and Goyle; Barty Crouch into Mad-Eye Moody for a whole year; Crabbe and Goyle as random students in Half-Blood Prince; the seven transformations of the Order members into Harry; Ron, Hermione and Harry into Ministry employees to find Umbridge and the locket... you're focusing on the one time in the books where it went wrong and forgetting that that's far outweighed by all the times it went right.

And the point of the animagus transformation is to turn into a non-human animal anyway.

If you're going through the trouble of changing into an animal, I'd guess you could take care of creating a suitable environment for it, first...
Or just.... transform into something that could live within your present environment?

But I don't know, necessarily, that you can control what kind of animal you would turn into.  The best guess at this point is that it might be based on some aspect of your personality.  There may be limitations on the spell that we just don't know about because they never come up in the books.

Breasts, I guess, are also, usually, not seen as weighing anything significant, right? But I can also foresee a mindless person bumping them into something unexpected...

...

I would expect this kind of assumption from a guy. Bumping into things, really? LOL

As for the weight issue, I've actually been wondering about this for personal reasons...

I know some women have large enough breasts that it causes separation of the ribs in their backs and other general back problems, so weight can be a significant thing.  This is at least one reason why breast reduction surgery is an option some women choose.  Having boobs can be a real drag.