Travelling with wellington boots in your luggage does indeed take up significant space and weight. I think what the right choice for you is depends on a number of factors:
- How picky are you when it comes to the shoes you walk in?
- Are you likely to find a pair that will fit you wherever you're going? (And bear in mind that in parts of the world (South America, Asia) the idea of a `large size' may be quite different from what you're used to, and that also includes calf size.)
If you are not too fussy and your size requirements aren't unusual for wherever you're going you could go with the `buy local' option, and maybe just bring a set of insoles. (Certainly I find walking on a flat footbed painful.)
Prices are likely to be low in many parts of the world.
If you are more demanding, or if you're worried about size issues, then I would second the recommendations already given: Worry about getting too hot. A format such as Muckboots (which have a stellar reputation) might allow you to fold over the shaft of the boot when you're not going into deeper water, and that may well help with temperature regulation. I used a wellie following a similar concept in the Amazon and it was definitely more comfortable than other wellies I'd used in the past, in particular the `cheap local' option.
I would also recommend making sure you try out the boots while you're still home, and that you experiment with insoles.