Getting from Phuket to Koh Samui

I%26#39;m hoping that the Thailand experts can help me here.

My boss is wanting to travel from Phuket to Koh Samui in July.

Can anyone recommend a good transfer company that I can enquire on his behalf as he doesn%26#39;t want to travel to Koh Samui by air (which would make my life easier) or by bus or train.

Thanks in advance for any assistance :)