I had 10-15 hours of lessons in the UK and passed both test the first time around (manual).
I had driven both automatic and manual in the US for 13+ years.
DH suggested I try a few instructors before settling on one. I'm glad he convinced me to do that because my first instructor looked great online and had wonderful reviews, but when it can to MY lesson, she hadn't thought of the fact I'd be on the opposite side of the road, the opposite side of the car and a few other 'switches' I had to adjust to.
Not a good lesson for sure.
And not my fault.
I tried another instructor (recommended by someone else on UK Yankee in South London) and he was great! He'd taught loads of other non-UK citizens and was familiar with driving on the 'opposite' side of the road.
He's got a home in Spain, so he's got regular experience making the switch himself.
It's amazing how much difference an instructor can make. You don't have to take lessons from someone you're not comfortable with (it's amazing how many people don't like their instructor yet keep giving them money!).
Even if you've got a patient and supportive instructor, it won't hurt to try someone else out.
You never know what's out there.