Most uni's do tend to offer single sex accoms and even if that's not something that they advertise you can always request it and if others also do they'll put you all together. I go to Durham and the college I'm in have a women's only wing they've also got single sex flats too at other colleges. it really depends on the university and how they manage their accommodations but it really shouldn't be an issue. If you're ever in doubt or if there's a uni you've set your heart on it's always worth contacting them. They try and accommodate for as many people as they can and you definitely won't be the only person looking for single sex accommodation.