We tried heaps of stuff with DD from the age of 3. Like you I felt pressure and was so stressed about it and i'm sure this was rubbing off on poor dd.
DD was dry during the day from 3 years 6 months. We tried 'normal' potty training for a couple of days where dd would wear no pull-up. She didn't wee once in the potty or toilet BUT we learned that she could control her wee's really well as she held it in for ages and ages to avoid using the potty. But she was very stressed after two days so we let it go.
A month later we put a clear plastic bag in the loo with chocolates, crisps, stickers etc and said she could have one item if she just sat on the loo, didn't have to do anything. We attached a pink seat with handles (part of the Disney princess 3 in 1 potty seat/step) and she would sit there but nothing would come out.
Then one day my husband came up with the brilliant idea to put a long mirror in front of her whilst she sat on the loo and she was fascinated with seeing herself on it and she did her first wee then! That was it, once she did it, she got it and was dry after that, probably only one accident since May.
Poo's however were another story...she only started using the loo for that last week and let me tell you, you'd have though we'd won the lottery! LOL!
For our DD it was a very very anxious thing, we're amazed at how chilled out she is now, I don't even think we realised how stressful she was finding the whole thing. We did use the 'Poo goes to Pooland' book which someone kindly emailed me. If you'd like a copy of it (its a pdf book and hysterical to read!) send me a message and i'll email it to you. The first time I read it DD freaked out. But we persevered and eventually she seemed to like the idea of her 'poo going home to Pooland'.
For me, it felt like DD would never ever get it. And then one day it just happens and you look back and wonder why you worried so much. Sending pixie dust your way so it happens soon for you guys too :)
BTW, I disagree with those who say wait until the communication is better. I have a friend with a child who is on the severe end of the spectrum, has no language at all, is only starting to use PECS now and he was toilet trained in 3 days before he turned 3!!! Each child is different so only you will know if your child is ready or not.