First off owning tack will be addin fuel to a fire that is already burning!
My hubby rides in a 16" with a sueded seat... It didn't keep his tush in the saddle when a turkey flushed and the horse ran/spooked out from underneath him. (sounds like what Fritz did to you with the water)
Saddles don't come with seatbelts...You're gonna
eat dirt from time to time.
I would look for a 17" then. A 1/2" won't be of much service...that can be taken up with the high cantle. Perhaps that's why I don't mind the mid range cantle...it allows for spillage.
My tushie has seen smaller days too.
Technically you should be able to fit a fist in front of you...I think behind you too...but that's not always practical or able to be done.
I would just make sure you're comfortable...I'm still on the look out for a 17" for myself, I'd like a bit more room too...I like to take lots of stuff with me and *sigh* I'm still a smoker and my smokes get squished in my back pockets..lol...Not much of a reason to buy a bigger saddle but hey...LOL.
Synthetics can be good first saddles too. I have a fabtron that is a good saddle tho it is almost too narrow in the gullet for my horses. I like the fabric fenders...There is very little fender torque with the fabric fenders and that eases the pain/strain on the knees.
I know Abeta makes a synthetic saddle in an 18"...I have seen it at a local farm/tack store. Seems to me it ran less than $300...I can't remember the exact price. AND that was for brand spankin' new.
Vida rode in an Abeta for a while...if memory serves it hurt her butt after a long ride. I'd ask her for sure rather than depending on my memory why she switched over to a custom saddle. There are many manufacturers that make seat cushions tho...
There are SO many things to take into consideration when buying a saddle and it's hard to know what you will like until you have actually ridden in one for a while. It has to fit you AND the horse. If it only fits the horse it could be throwing YOU off balance and effecting the horse's performance.
If it only fits you, well..same goes for the horse....It's uncomfortable and hurting him too.
Just make sure you aren't paying too much for the saddle. That way if you need to sell it, you won't be taking a huge loss on it.