I do remapping using Viezu maps. They are tried and tested and reliable - as well as being insured. If you put in the vehicle details on the website https://viezu.com/
, it shows an increase of 35bhp and 70Nm of torque for a price of £324+VAT. That gets you slightly over your 140bhp target.
You may be able to find an installer near to you who will charge less than the head office price (we don't add VAT, for instance).
There are obviously other map suppliers out there, some offering what appears to be more for less, but we chose Viezu because they have a decent track record (they mapped 24,000 vans for BT).
Hope this helps