Firstly, I am very sorry you are finding it difficult to get a dog. I have struggled too recently despite being a seasoned dog owner but that comes with wanting a certain pedigree breed. I grew up with spaniels all my life until fairly recently when I changed to sighthounds, which for a lot of reasons I prefer to spaniels.
I can help you with Cavaliers but please do not get offended, I mean this to be helpful. My family has had cavalier for 30 years now after owning other types of pedigree spaniels that just became too demanding exercise wise and maintenance wise. Cavaliers are much more chilled than other spaniels where there is a working line (think cocker and springers). They are proper lap dogs and do absolutely nothing. In my opinion they are lazy to a fault but that is subjective. They are also very affectionate.
Here is the but, they are really not smart, which might not be a problem for some but it is for me. I don't see them being a therapy dog else than as a living teddy bear, which they are very good at. And there is the maintenance, a cavalier groomed properly needs plucking, not shaving regularly (at least once a month). Then the eyes and ears need cleaning. It is a proper faff.
However, the biggest but is that like all breeds that have been popular, they are so inbred you will struggle to find a healthy one. All of ours have had an issue of some sort, mainly heart, eyes and breathing. Cockers and cavaliers, in my experience have been tempered with to a point of near no return unless they are from a working line (and even then...).
Reading your post, I would strongly advise against any pure breed unless you find one that has not been popular and is fairly common here, therefore a good uk breed. BUT you will be getting a puppy, and this is a roll of the dice. Any breeder that says they can match you to a puppy is lying. It is not possible. It is like looking at a child, a toddler and predicting they will be something or other.
I would also advise against those designer cross breads (mongrels really) that are everywhere, any -chon or -oodles or whatever new fashion has cropped up. You are getting into totally uncharted territory. Why pay the price of a full pedigree for a mongrel? Get a rescue instead for a fraction of the price.
Therefore, your best bet is to adopt a grown up dog that has been tried and tested by the rescue, ideally fostered. This is the only way you will know what you are getting yourself into. Have you considered a greyhound? They are so many desperate to get out of kennels and they are lazy.
Finally, I mean this in the nicest possible way, do you feel you can really take a dog on? Dogs are sensitive and are not easy. Something somewhere will go wrong, can you mentally cope with that? I say this because the consequences of owning a dog could become far more costly mental health wise than not having one in the first place.