Hi there Kieran
DIY contact lens prescriptions are never a good idea (although all too many of my friends just whack in an order online, year in, year out, for daily disposables without ever going for an up-to-date eyesight test

) especially for a product as complex as Kerasoft ! You'll definitely need find an optometrist with experience in prescribing this type of lens.
The good news is that many NHS eye units are prepared to offer this option to you. But alas, not all. The only way to be sure is to ask.
If the eye unit you attend within the NHS isn't going to be able to let you trial these then, firstly, I'd nag them into changing their stance. I think it's so important for Keratoconus patients to have a voice in their treatment. Even if a particular product isn't suitable for you, unless you give it a go, you'd always have that doubt. I think psychologically, that's not a good place to be.
If the initial NHS provision isn't what you want, you can ask to be referred to a different eye unit who are prepared to dispense Kerasoft (or any other lens type you're interested in). The drawback is, that might end up being some distance away from where you live. It's not really fair, but ultimately, you just have to travel if needed. That's why I'd encourage patients to ask for the services they want where they want them because otherwise, we'll get the lowest common denominator... But I do appreciate, sometimes you simply don't want the aggravation of a battle with an intransigent NHS Trust.
Finally, there's private practice. Expect to pay around £250 per lens, but most of that covers the optometrist's time and contribution to their equipment and premises overheads. I'll probably be shot down by any NHS optometrists but private practice tends to bring other advantages such as much greater flexibility in appointment times and far greater "chair time". More time with the optometrist can mean better outcomes. That said, many, many people get first rate care from the NHS.
Anything else you need to know, just ask. Hopefully people with real-world experience can help with what they've found in first hand usage.
Cheers
Chris