Join me in wearing trainers to work and then change into heels. Who knows, maybe we can start a new fashion craze. As for fit, if they aren't comfortable, don't think they will become so with wear. Also, don't buy shoes based on what you think your size is. Start from there, and if you need to go up a half size, do so.
Brands vary in size.
Go by what feels like it fits. Your feet will spread with age, so make sure that you have both feet measured every time you buy shoes, and buy for the biggest foot. Go shopping in the afternoon as feet tend to swell as the day goes on. Make sure that you dry your feet thoroughly, especially between your toes, after bathing and sprinkle on a little powder to keep your feet dry. This will help to prevent athlete's foot.