Does anyone have any advice on where we could start the search or can recommend? Ideally we would like a Cavapoo but am open to other suggestions,
TBH OP (and I mean this VERY gently) if you want a Cavapoo but you're 'open to other suggestions' then I don't think you've done anywhere near enough research. You say you're mindful about not using a dodgy breeder. Good. But with mongrels you cannot be sure that they aren't coming from a dodgy breeder. Word of mouth means bugger all - backyard breeders are smart. They play on your emotions of 'oh isn't it a cute puppy, I can't leave it here'. They hide what they are and, unless you know what to look for, it can be hard to tell the ones who are just a bit shit to the ones who are downright cruel.
You need to have a think about:
What size house you have
What size garden you have
How much attention you can give a dog (puppies need constant supervision for months and month). So, realistically, if you're gonna bugger off out all day or be away for large parts of the day you shouldn't get a dog (it's going to make training it hard and just be cruel IMO)
How much you can exercise it (a cavapoo is part cavalier and part poodle, so despite being small will likely still need a lot of exercise and mental stimulation - they are SMART dogs)
How long you're willing to commit for - some dogs only live 8 years (St. Bernard), some live 13+ (Collies/Cattle Dogs)
How much effort you're willing to put into training. Do you want a dog that will quickly learn commands BUT will require far more mental stimulation? Or do you want a thick twit?
How much you can afford to spend on upkeep (my retriever costs me £250 a month to feed + £40 insurance + £60 grooming + probably £50/60 on toys [he likes pulling out the toys innards cos he's a little thug] + other misc costs).
Will you have children/if you already dog what age they are? Are they old enough to understand about giving a dog space etc?
Is now the right time to actually get a dog?
You need to research potential health complications (i.e Spaniels can get serious eye problems, ear problems, patella problems, they can be aggressive. Goldens have a high chance of getting cancer, can also have significant problems with joints etc) and consider whether you are prepared to take that risk.
Ultimately, I would go with a KC pedigree from an Assured Breeder because they offer lifetime support and commitment. You (should) sign a contract that lays out what to expect and they will run tests so you know your puppy is as healthy as can be. Most mongrel breeders don't do that IME.
Finally, and, most importantly: WHY do you want a dog?
A dog is a huge commitment. Every breed is different and comes with different issues/commitments/rewards and if you are not fully fixed on a particular breed but are open to random suggestions...I'm not sure you've really thought this through.