Non-dormer loft conversion - advice sought

[Nigello]

Has anyone got first-hand experience of the above?

If so, which firm did it and what was the cost (and when)?

Extra space would be good, but not at all vital, and I would prefer to keep costs and mess down. Also, a loft converter told me the space would be very low without either raising the roof or lowering the ceiling of the first floor - things I would not want to do at all.

Thanks