If the floorboards are SOLID and are adequately screwed down, you may also want to consider using Ardex-flex 7001 after priming with Ardex P51. This is called the Ardex Timber System and is designed for this type of job. It is mixed quite thin to ensure a solid bed fixing and is a single part mix. Has about an hour life in the bucket and can be grouted after 2 hours.
You can get away with a smaller notched trowel too, depending on your tile size.
