Hi Freddie,
First of all, very sorry for your loss.
I have two labs, my oldest (yellow) is nearly 5, my youngest is 3 (black). They are my first dogs, but I have found them to be a lovely breed - hence my nickname! Well trained, mature labs are capable of being placid and loving at home (and gentle with children), but active and lively enough to really enjoy a long walk and/or swim. They are an intelligent breed, very trainable and don't generally have an agressive nature (although my older dog has a booming bark). I can leave mine generally for up to six hours. I wouldn't really be concerned about their behaviour if I pushed that a little longer, but I really don't like to do that for my own peace of mind. They do go to "doggy day care" when I am at work though through choice.
I take them to training classes, which are a mix of obedience, aglitlty and search/tracking work, because they do need things to occupy their minds.
As a breed, they are notoriously greedy and you have to watch their weight. They are deep chested dogs, so are at risk of bloat. In order to keep them safe, you need to give them two smaller meals a day, and not exercise them at least two hours after and an hour before a meal.
The main health problems come from a tendency to hip displasia, although recent breeding has meant that elbows can be more of a problem. There are also inherited heart and eye conditions. Any good breeder will have fully hip and elbow scored the parents and have had the necessary heart and eye tests done. Check the kennel club web site for indications of a good hip score for the breed. If you get a puppy, you need to plan on their first 18 months being gentle walking only, avoiding heavy impact/stairs/abrupt changes of direction/too long a walk to make sure the hips develop in a healthy way - although try telling that to the dog!
Labs mature at around two years old - so they have a long adolescence -and can be quite boiserious if not exercised/trained/socialised. Be prepared for a potentially tough time for a few months with chewing/jumping up/counter surfing and mouthing. This is where training and lots of things to chew on will be useful. Controlling the dog's natural exuberance will be the main issue. We used crates to train ours and this did keep them safe and protect our furniture when we needed to go out!
There are almost two types of labs now - show lines (think the chunky, stocky dog) and working dogs. Mine are from working dog lines. Finer boned, slightly more highly strung but having the stamina for long walks and lots of activity.
Labs were originally bred to bring in fishing nets. They are born swimmers and as such have webbed feet (so you need to regularly check between the dog's toes for grass seeds etc) and a double coat. This means they do shed quite a bit but it is manageable with brushing. They don't need a bath too often (unless they get in something stinky).
Generally, they are affectionate, curious, loyal and fun. I wouldn't be without mine, but I have the time to take them for long walks and train them. Young dogs/puppies in my opinion would not really work in households where they won't get at least an hours/attention exercise a day. Adult dogs are much more manageable than puppies if you put the groundwork in.
Anecdotally, black labs are the more intelligent of the labs, which can either be a good thing or a bad thing, depending on whether the dog wants to work with you!
Picking a breeder is not something to rush. The relevant medical tests are essential, and the usual tips to avoid puppy farms, including being able to meet the parents, and see them with the pups, seeing where the puppies are being raised, kennel club papers and just the feel of the place. Our dogs have the same mum and came from the same wonderful breeders who raised them in their family home on a working farm, fathered by a gun dog of a really good pedigree. We paid between £400 and £450 for our two.
Hope that helps!