Simples - go to a reputable tuner (advertisers on here, Revo, AMD, Custom Code, Jabba Sport to name a few but not all!!) and give them around £300!! That will get you to about 190bhp depending on the tuner and how they configure their maps. Exhaust, filter add a little more to the mix and don't forget to consider brakes and suspension too.
Revo is quite peaky - ie boost comes in hard and fast and tails off fast too. Others tend to be less peaky so you get more power earlier and for longer although the headline value may be less than Revo. I happen to like the peaky Revo code myself, others prefer the flatter torque curve of others.
You will need a clutch at some point on a PD150 car. The torque of diesels soon has the standard one slipping. Budget £800 for a new one to do it properly (I tried to do it cheaply and it just doesn't work), or have the car "custom" mapped by one of the tuners on a rolling road but to lower torque figures to prolong the clutch. Revo doesn't allow you to do that - you have been warned!!!
Lastly - search on here for others experiences as there are loads of opinions and views but in the end is very much down to the service you receive at the tuner and personal preferences on how your car drives or even simply a case of a tuner being closest to where you live!