Katy, I am so very, very sorry you are having to go through this. I do not have personal experience but I have worked professionally in this area. First thing, i would endorse Aloha's suggestion you contact Antenatal Results and Choices (ARC): they have a good reputation and will understand what you are going through.
If you do opt for termination, you should go with your instincts on the method. Undoubtedly surgical termination is easier at the time, but if you will be haunted by the process then it may well not be easier for you in the long term. Also, it can be hard to find surgeons who are (a) willing to do it at this stage, and (b) have had lots of practice in doing so (and it is that practice that makes them skilled at it).
If you do have a medical termination, it shouldn't be a horrific physical experience. You will of course be very distressed, but you will be offered pain relief and sedation. With later terminations (20 weeks plus) you would be able to dress and cuddle your baby, if you want to, and to have photos. I don't know what practice is with a baby this age, I'm afraid, but do ask for all the details so you will know what to expect.
There is another good organisation called Support After Termination for Foetal Abnormality who can give you support afterwards.
Again, I am so very sorry you are going through this. A good friend of mine went through a similar experience recently and I know how very painful it is. I will be thinking of you.