I brought my queen size American bed.
There are two things to watch out for:
1) Will it fit through passageways and up stairs to get into the room where it will remain?
2) You will never find sheets here that exactly match, but these things are also not insurmountable.
I am seeing larger beds come into being here, however, and I do wonder if a time comes when we will see American standards be options (like those companies advertising American fridges). Grange (though I don't think it's originally American, I see it as an American company because it's rather prevalent there) is making inroads here, for instance. Their great big beautiful massive wooden sleigh beds are easily found...and I suspect they've kept American sizing. I'd be disappointed if they haven't, and certainly the man representing them in the shop I went into was American.
Back to my own 'adventure' with my bed. It's wrought iron and there was no way I wasn't going to bring it. Being canopy posed a problem, but it did unbolt in parts so I didn't give it too much of a think...until the day it arrived. It would not go upstairs. It would not go through the window. It just was not going, period. So I took out a hack saw and cried the whole time I 'made' it fit. Then the whole thing got bolted back together. No quite soldered, but with having fabric draped all down, the 'scars' are well hidden.
Sheets. Take a look at a piece of American letter-size paper and hold it up against the equivalent British standard of A4. One's too long and the other's too wide, but by smidgeons. Enough to make it frustrating. Buy your sheets in the US. Next trip to the US, buy more. For me it took about five trips to Bed Bath and Beyond before I got curtains, pillows and cases, bolsters, drapey things for the bed, duvet covers, sheets, etc. that all matched (thank goodness they kept the style for a few years running).
It is my
personal opinion, and I hope I don't offend anyone: I find that the styles available here are limited. You can have five different high street shops selling sheets and curtains and they all sell the same design. They seem to be stuck in purples and silvers, or limes and oranges, or royal blues and golds, in styles of scripty writing or angels, swirly bits or vertical stripes. Lovely material, don't get me wrong. But it's so much the same that it's getting real old. I've been seeing it for five years now.
It's an individual taste. And my taste is very much within the brocaidey, dripping old money, stuff. (Hey, it's nice to dream, huh?)
I rambled...it's Saturday morning.

My point is that you need to make sure your bed will fit
into your home here. Next, buy your sheets in the US.
If you want a size comparison, or you want some custom sheets made for your bed, try this site:
UK and US mattress sizes(Seems somewhat silly they didn't do eqivalent sizing cm vs. in.
Check out Leah's sizing chart:
UK Yankee Conversion Tools(Just noticed: this link is to a place that's just up the road from me...5 or so miles!)