I'd like to add to the discussion about the cause of your issue, as this page is indexed highly in google:
If your problem is only when the engine and gearbox are cold, and the 'box performs fine in all other respects then it may be that the synchromesh's in the gearbox are starting to wear.
The reason this causes poor cold gear changes is thus: when the gearbox oil is cold, the increased viscosity of the oil, combined with the worn frictional surfaces of the synchromesh will prevent the generation of enough frictional force for the syncro's to do their job; that is to match the speed of the input and output shafts (which then allows the selector forks to slide the gears effortlessly together).
Warmer oil is thinner and allows the frictional surfaces of the syncro's to perform properly.
To rectify this you could look at changing to an oil of the same type, but with enhanced viscosity additives that help reduce the viscosity of the oil at lower temperatures.
Simply replacing the oil may not help as the high performance synthetic oils used in modern car gearboxes (and engines) are less prone to wear (hence most gearboxes are sealed for life).
Accordingly, you may be able to find an additive to add to the original spec oil that may improve cold performance.