'Jonesey' is right. Buy a high quality paint from a Paint Retailer. (Found in the Yellow Pages under PAINT - RETAIL.) The same goes for a good primer.
Generally speaking, the bubbles are caused by moisture being trapped under the paint. When it is heated, it expands and causes the paint to bubble. The only way to fix this is to 'pop' the bubbles and remove any loose paint. Then, apply some spackle to the 'damaged area', sand, prime (twice, with a high-quality Primer), and paint. Yes, as Jonesey says, make sure you stir the paint real well. And make sure you don't use the room for at least 24 hours (since it is a bathroom which generates moisture.)