Comfort is quite subjective.
Go to some big box stores or any where else for that matter where you can pick up, look at, and feel different makes and models of mice.
Try mice from friends and family. Find two or three (hopefully) that are acceptable and then look for product reviews by independent sources (such as Tom's) and also reviews by verified purchasers.
Then go to the manufacturer's websites. Look for and read the User Guide/Manual. Read the manufacturer's forums and FAQs.
See what people are asking and complaining about.
Pay attention to what is said as well as what is not said.
Most likely you will be able to select a mouse that suits you.