I'm going to say something that everybody knows but it is a necessary reminder in these situations:
A dog is not just something that is cute and fills your empty moments with fun and then disappears into a void until your next empty moment. It's not like your friend's dog that you hang out with for a few hours every couple weeks and think oh that was fun. It's not an accessory.
It is a living thing and lifetime commitment. It needs to be fed and get exercise and have its shit picked up - every single day for a couple of decades. Doesn't matter if you've had a long, hard day at work - the dog will not give you the evening off.
It is much higher maintenance than a house cat and yes, if you have a cat, it may upset things very much. Some cats are accepting but some will have their life ruined by it and never recover. Doesn't matter if it makes sense. It's a cat.
A dog may have complicated health problems requiring many trips to the vet for years, costing thousands and even 10's of thousands of dollars - and breaking your heart in the process.
If that all sounds acceptable, then great. There are a lot of dogs that need homes. Personally I recommend getting a mutt rather than a specific breed.
