Congratulations on your engagement.
I would strongly recommend you do a low key registry office job in the UK and then just a symbolic ceremony abroad. This will avoid any issues around the legality of your marriage in the UK. Also, if you choose to get married in a non English speaking country, your marriage certificate will be in a foreign language. This means you will have to get certified translations at around £50 a pop every time you need to prove you are married in the UK. (If you're planning to change your name on your passport or any other ID documents, this will be an issue. If you're planning to keep your name, less so.)
Please be mindful of the fact that a lot of people take a bit of a dim view of "destination weddings" where the couple have no obvious connection to the country. You will be asking people to take annual leave and spend potentially a lot of money to attend. Some people just won't be able to do it, for example, if they are teachers or have kids and you don't do it in the school holidays, or just if they don't have the money.
If you're definitely going to do it, I suggest picking somewhere which is quick, easy and inexpensive to get to from the UK. Think France, Spain or Italy, not Thailand or Bali.
Bear in mind that you're going to need to make several trips out there to check out venues and make all the necessary arrangements. If you don't speak the local language, do you know someone who does who would be willing to help you? Think about what you will need to transport over there - the dress is a big one. Assuming you'll want to buy it in the UK, for fittings etc, I would suggest choosing something fairly simple and easy to transport, rather than a big princess dress with massive petticoats.
If you choose a venue which isn't easy to get to by public transport (most chateaux in France really aren't, for example), then think about putting on a bus to transport your guests there from the nearest town or airport. Asking people to travel abroad for your wedding is a fairly big ask, so make it as easy and stress-free for them as possible. If it's a fairly small wedding, consider trying to find a venue with on-site accommodation for everyone.
Finally, depending on when you are planning to get married, think carefully about Brexit. If you've only just got engaged then you're probably not going to do it next summer, but if that is what you're planning, bear in mind that flights and foreign travel in general might be disrupted post Brexit day, and if the pound tanks after the end of March you might find that everything is much more expensive than you (or your guests) are currently anticipating. No real advice on this point, other than to just be aware of it, and don't book anything soon after Brexit day or commit to spending large sums of money in a foreign currency before we have a clearer idea about what is happening.
Good luck!