I've had the same problem using postcodes to find customer sites, as they can often be half a mile or more from where you want to be.
I always use the DMS co-ordinates. Before finding an app to convert from digital format, I made an excel spreadsheet to do it. Bit of a faff, but it worked.
These days, if I'm going somewhere I haven't been before, I use google maps to locate the site, streetview to find the entrance to the car park, or whatever, then drop a pin in the map at that point. That then generates digital co-ordinates (first pic) and if you click on them, it gives another box with DMS co-ordinates.