Howdo.
Courtenay, Regal, Midpoint Garage and Thorney Motorsport are the big players I know about in VX tuning.
Depends on how much you want to spend. You can remap your Corsa to 159bhp and 340Nm of torque for just a couple of hundred quid from someone like Midlandremaps, that I've used before and gave me a good map for my Focus.
Intercoolers can be a grand or more, plus because they allow bigger gains you might need to think about upgrading your clutch too.
That said the people above might do an all in deal where you get an IK, filter and remap all together.