I have had greys for 11 years, and I still get nervous about adding another to my home. It's normal to have questions or feel like you need to second guess yourself. I did that when we got Franny three years ago. I did it again when we got our foster last May. These feelings went away within about a day of the dog being there.
Maybe what you need is to adopt a dog that has bounced, meaning one that has been in a home for awhile and is being returned, or maybe an older dog that is a bit more laid back that will be content to curl up on your couch and just hang out with you. There are plenty of dogs like that need homes too. In fact, all three of mine, and my fosters have all been bounces. They need homes and love just as much as a new off the track dog does.