I'm sure there are loads of cats in the Essex area who would answer to your description. Many cats are branded as not good with dogs or children but often they have never associated with either. In my experience dogs and cats get on fine together unless the dog is one of the more aggressive terrier breeds or fighting breeds. In fact, it is usually the cats who rule the roost. If you buy a gundog breed (loads to choose from....) I don't think you will have any trouble at all. And at the moment you don't possess a dog so who knows what will pan out in the future.
Historically, I always had dogs until my hubs bought me my first cat. And then I couldn't imagine how I'd ever lived my life without one!! But this was a complete surprise. It was not something I had been pining for...(it would have been if I'd known how smitten I was gonna be). So the dogs just had to come to terms with their new friend. Well, within an hour the kitten was snuggled up with both of them and trying to suckle one! That was some years ago now and Emma was my beautiful and incredibly gentle English Setter who became a sort of surrogate mum...and seemed to love it! She passed away seven years ago but all my dogs and cats have got on famously and still do...
I know many other peeps on Purrs have both cats and dogs...and children..and experience zero problems. I wouldn't mention your future ideas when visiting the shelters but wait and see which one of the little babes captures your heart. And take it from there....
There is definitely a little sweetheart in one of those centres waiting for a visit from you.
P.S. Whereabouts in Essex are you? Have you tried the Pussycat Lodge near Brentwood? Jenny runs it and is a lovely person. Here's a little excerpt from her website which I think is just delightful:
'When things just get too much Jennie reminds herself of a Christmas when a little feral cat from a pen roof, too frightened to venture into the house previously, was waiting for her on Christmas morning under the tree playing with a fir cone, a sight as welcome as any Christmas present. It's moments like that that make it all worthwhile.'http://www.pussycatlodge.co.uk/