I have a 14.2 Dales pony called Sam. I'm 5 feet 9 inches tall and weight about 10 stones.
The breed standard for Dales ponies says that they used to carry the lead from the mines (up to 17 stones) for 200 miles each week. A pony of this type can easily carry someone much heavier than you so you've no need to worry!
I went pony trekking with the Dales pony trekking centre at Malham last year. Some of their ponies are a lot smaller than Sam and carry men out trekking for a full day without any problems.
Ignore the nasty comments - they're only jealoous you've got a Dales.
For the record, there is also a great website at www.dalesfans.org
Everyone is really friendly and you'll get great advice - same as you do on this one!