The Spydercos are excellent but quite pricey and tactical-looking.
Thumb studs are an alternative. Various manufacturers use them.
Similarly, a small disc on the spine near the pivot works well. Shing (on Britishblades) makes some like this.
Most Friction folders (like the Svord, above) can be easily opened one handed. I have one that also has a spydie-hole. Personally, I don't get on with friction folders.
As you say, lots of choices- how much you want to spend and whether you want to be "UK EDC legal" will help narrow it down.