Sounds like you really don't have much idea about dogs so please please get advice from a vet before you decide anything as there are lots of different considerations to take into account eg. do you have a garden, how big is the house, have you considered the cost, are you aware how much mess they make with hairs, muddy paws etc., what about the dog when you go away on holiday or for the weekend ?
Rescue places such as Dogs Trust will also be able to give you good advice.
Despite all I've said above, I wouldn't be without my mutts and once you choose one it is most definitely part of the family. Oh, and whatever you get will need exercised 7 days a week and once a day as a very minimum, even small breeds.
My 2 'boring labs' at about 4 months, nearly 4 years old now and NOT fat. They are also about to come out with me on the bike so I'll try and post another pic to confirm you will not need to give up your cheeky daytime rides :D