I'll also give Premier Seeds a thumbs up. I've ordered from them the last two years and have had much success. The one place which I have found to be fantastic is
Sea Spring Seeds. I made a point of testing a good few UK seed/plug/plant suppliers with emails, and both Premier and Sea Spring delivered on the customer interaction side. Sea Spring Seeds just did more for me on the chili side of things, so that's where I went back to this year. They also cover some more esoteric (?) things to try, and actually encourage seed saving; so go figure where I spent my money for this year of growing.
I have no ties to Sea Spring, or Premier. I'm just a semi newbie grower, and figure Thomson & Morgan etc... can sit this season out. When I first started to look at what was available, I found independents had the greatest range of fun stuff, and so far I haven't met with lesser germination or produce difference. If anything, I'd say more healthy plants. Probably because the seeds aren't stuck in cold storage for how many years.
Just my experience so far.
As for raised beds. It would seem practical with your trees, but I couldn't comment for sure. Whatever you do, please don't cut down your fruit trees to make room for vegetable beds. You can grow a turnip out of my belly button (sticky in), but a fruit tree... nah, I think you would need to do some hard grafting work to get it to comply.
In other words: Create the space, but don't lose the grace!