It's hard to know where to start with this!

You say "sportsboat" but of "J24, Jaguar 21, Sonata or Hunter 707" the 707 is the only one that most people would call a sportsboat and plenty would argue with even that. J24 is better described as a racing keelboat, Jaguar and Sonata as a small cruiser-racers. 

"The option of having a week or weekend away with the other half in some degree of basic comfort". Hm. Ever spent a night in a boat this size? They are very tiny and very cramped. They are also usually wet and smell of a mixture of mould and outboard fuel. I am not a 5-star hotel person and actually enjoy camping but I would go a long way to avoid sleeping on any of these boats.

There is no sailing of this kind around Bristol. There is a certain amount in Cardiff Bay but I'd suggest you are probably looking at the Solent or Poole (and maybe Burnham, about which I know little). You have almost zero chance of getting a deep-water swinging mooring in the Solent unless you are a club member (with long waiting lists) or live in a local parish that owns some moorings. You can get tidal swinging moorings but it is hopeless to keep race boats on them and only bilge-keelers are suitable. I'm not that familiar with Poole but suspect the remarks just made also apply.

Class racing: 707s have class racing in Hamble and Burnham. I believe J24s have class racing in Poole. Sonatas no longer have regular class racing anywhere and I don't think Jaguars ever did.

Budget - well yes you could probably get any of these boats for £6,500. But buying is just for starters. I owned a 707 on the Hamble for a number of years and my annual running budget was around £6,000. OK, I spent a fair amount on  sails but you couldn't be competitive on very much less. I've had conversations recently with SB3 owners on running costs and their budgets are much the same. You could run a small cruiser on a lot less but for racing, sorry but to keep a competitive racing keelboat on the Solent, think in terms of at least £6,000 annual running cost. If you can do it for less, well that will be a pleasant surprise.

Trailer sailing: yes you can but few do these days on a regular basis, because it is such a faff and public slipways in the Solent are few and busy. A lifting keel is a must, which only the Jaguar has. You also kill your trailer dunking it frequently in salt water and you need somewhere at home to store the boat. Many SB3s trailer sail but this is a substantially lighter boat than a cruiser-racer type and they mostly launch from club or marina slipways, which also costs. 

My advice: if you want to cruise, think about cheap flights to somewhere warm and charter something a bit bigger a couple of times a year. Your other half is likely to enjoy this a whole lot more than weekends crammed on a tiny boat in the UK.

If you want to race, get on a few boats as crew (which is easily enough done with a decent dinghy racing CV). If you learn something about the scene, you'll be better placed to make decisions if and when you decide to buy.