Would say go with the H2B or full H22 swap. Basic breathing mods and a remap should see you into K20 territory with plenty more torque and still with an internally standard engine. Once you have done the hard work and completed the conversion your sorted. If the motor dies you just replace it with another. H22's are cheap peanuts these days.
B18 is an easy option but can be costly if your not saticfied with 200hp and 130lbft. Also If you decide to tune (which you most likely will) you have a tuned engine so will cost alot more to replace or fix if something goes wrong.
Don't think colorado is in the UK....