These are the pair of cuffs that I used for several months before I was brave enough to attempt my real handcuffs:
http://www.amazon.com/gp/product/B0006GKB4S/ They do have a small safety catch on them for that extra safe feeling for those not so daring. I used them a lot and they never broke and I think they are even thicker than my real handcuffs haha. The latch is also smaller than what I have seen on some other toy handcuffs. If you have had issues with cuffs being too small for you, these might also be too small, but I have smaller wrists so I don't notice.
I do second what others are saying here though. Do get a set of real police handcuffs. You can find auctioned ex-police cuffs for sale on ebay (or gumtree) in your country quite often for around 10 quid at times. If you do get some, make sure they have fully functioning ratchets, some you will find don't operate properly anymore and that's why the police force auctioned them. You do get to practice opening up real handcuffs though and can practice that a lot; for those times when one of us ties you up (cuffs you up?) and you want to be devious and escape with that secret paperclip. Good to practice and learn how real cuffs feel and operate, even if you don't intend on putting them on yourself soon.
Cheers.