It isn't so long ago that the Which? organisation used to sell a little book called 'Wills and Probate'. They have stopped selling it now and instead offer this service at a fixed price of £89, or £149 for mirror wills
http://www.whichwills.com/
There are certain caveats about one having straightforward affairs, but this service operates by the output being checked by a suitably qualified person, but you may find it useful.
For those who believe that the Which? organisation consistently offers value-for-money consumer advice for the last 30 years, it could be useful.