I am often asked by people who are doing well in ridden show classes how they can make the transition into riding side saddle.
Side saddle is very popular now but you have to know what you are doing and it’s not something you can teach yourself. My advice is don’t assume that just because you like the idea of it you will automatically love it. It’s very different from riding astride; you can’t sit on top of the horse, you have to sit into the horse and learn to relax, soften and let the saddle absorb you.
Find a proficient side saddle rider with an experienced horse that carries a side saddle well and have a lesson or two before taking things further.
I was taught side saddle by a lady called Miss Sybil Smith who also taught the Queen! She had her yard in Holyport just outside Maidenhead which coincidentally was where I was based many years later with Carol Bardo. I was nine when I went to Miss Smith for lessons; she was a wonderful lady and a real stickler. She would ride next to me the whole time telling me what I should and shouldn’t be doing, how to keep straight and shoulders back. In particular the right shoulder as this keeps you straight and is one of the most important points to riding side saddle.
Having established that side saddle is for you, find someone to give you a hand to see if your horse is capable of carrying the saddle and get one fitted correctly. Getting it wrong at this stage is an expensive mistake.
It is worth speaking to the Side Saddle Association for recommendations for instructors, trainers, saddle fitters and so on.
When riding side saddle you still sit square as if you are riding astride, it’s just that your right leg is flipped over the pommel. Your seat bones, shoulders and hips should still be straight with the horse’s ears. This why having someone who knows their stuff is invaluable because it is easy to sit crooked and that in turn makes it hard for your horse to carry you and you can form bad habits.
Most horses take to side saddle quite well and are capable of carrying it. The most common reason for a horse not to like it is the balance strap that sits much further back than a girth (you do have a girth as well). Some horses are nervous about having 2 legs on one side or may be unhappy if the apron flaps. 
You need to have a horse that has the right conformation to carry a side saddle. For one thing, the saddle is longer, heavier and sits a bit further back. If a horse is short in the back they can feel constricted. Your horse should have scope and a good sloping shoulder otherwise you will feel like you are sitting on the point of the shoulder and that there is not enough in front of you. Ideally you want a horse with a good front that sits up when you ride it because a side saddle sits three or four inches higher than an ordinary one so you sit much higher up.
Make sure your horse is well schooled, free moving and doesn’t lean on you because if it is heavy in your hand you don’t have a leg on each side to be able to put your leg on to lift it.
There are plenty of places that sell well made top hats, silk ties (stocks) and habits. Personally I think you can’t beat the old fashioned hunting habits made out of heavy weight cloth and I’m always on the lookout for lovely second hand ones. You’ll need to wear a spur and carry a whip or stick in your right hand as that is effectively your right leg.
I have been unbelievably lucky to have some lovely side saddle horses. However I have chosen horses I would like to put a side saddle on hoping that they are exactly what I was after and there have been one or two horses that haven’t taken to it or not been as good as I had hoped.
Time to Reflect, the lovely mare that won the 2018 HOYS supreme, was absolute perfection and there is nothing better than riding a horse like that. She ticked every box from the start, just took to side saddle and loved it. She is a beautifully put together mare, lovely front, fabulous way of going, very comfortable and beautifully schooled.
So, if side saddle is for you and you have the right horse, there is nothing quite like it!