If you're not sure how to get from Singapore or Kualau Lumpur to Mersing, the ferry port to Tioman, then it's good to know that there are two public transport options: by bus and by car.
If you want to go by bus, then you can use this bus ticket booking form. You can select your own seat and your booking is confirmed instantly.
Alternatively, you can go by taxi.
Both means of transport have some pros and cons. The bus is obviously more budget-oriented, whereas the taxi will offer privacy, convenience and comfort.
Another great advantage a taxi has over going by bus is that taxi passengers can remain in the vehicle during passport control, whilst crossing the border into Malaysia. This also applies when going back from Malaysia to Singapore.
This privilege is not extended to bus passengers; instead, all bus passengers must disembark their bus, along with all their luggage, in order to walk to the passport complex escalators and then on to the passport control queuing area. This applies twice, at Singapore's passport control and at Malaysia's passport control.
In other words, your own taxi offers a good amount more comfort and convenience. Good to know.