First work out what sort of dog you want.
Look at the breed groups - gundogs, working dogs, utility breeds (this is the 'doesn't really have a job/we're not sure/no other category wants them lot), toy breeds, hounds and terriers.
Doesn't matter if you think you want a designer crossbreed or a good ole mix - start there.
Make a list of wants and absolute 'cannot haves' for physical or behavioural qualities (but keep in mind whatever the breed, they're all dogs and can all behave like dogs!).
Use this info to narrow down the breeds you'd like to know more about - remember seeing videos and photos of them is NOT in any way comparable to seeing them inside someones home (and ideally, a home much like yours).
If you do want a designer cross or very expensive mutt or cheap mutt - still do the above, because if you really DON'T like the traits of say, Cocker Spaniels and Poodles, then theres a bloody good chance you will not like a Cockerpoo. Crossbreeding does not guarantee the good points or the bits you like about each breed, you stand a similar chance of getting the bad bits or bits you don't like!
From here on, decide do you want to do your very best to have a healthy (mentally and physically) puppy and do the work and pay for that (on the understanding there are no guarantees but you can stack the odds in your favour).
Or do you not mind a bit of a gamble.
If you don't want a gamble, go find the Breed Clubs and Societys (just google 'xyz breed club uk') for your breed and they'll have a puppy person or contact the secretary. They can help you talk to breeders to meet adult dogs in their home or at shows, and you can start to narrow things down further.
They'll also help you learn about the health of the breed, tests that are necessary and other useful info about the breed.
Then you should if you go down this path, find a reputable breeder, producing kennel club registered puppies, from health tested parents (there will be records of these results, see them, have them explained to you, these are not a veterinary check to say 'yes this ones alive and healthy' they are specific to conditions and parents should not be bred with out them. Some are annual, some are one offs.) They should be bred in the home (there are a few exceptions to this) and the beginnings of socialisation and habituation to general family life should be started with the breeder.
If you want to take a gamble, you aren't bothered about what your puppy might look like or you want to take on an older dog and think you can afford to take risks with health - go to a rescue.
Because if you aren't bothered about KC registration, health tests, puppies being raised IN the home, socialisation, habituation, etc... but want a brand new puppy, then you'll be funding puppy farmers, commercial farmers of puppies as 'livestock'.
And in that case you might as well rescue their rejects and overstock at a tenth of the price from a rescue, which is where they and their parents will end up. Or hang fire until they are 10 to 18 months and the people who bought them on a whim will dump them in rescue - added bonus here is you know what they look like as adults!