Mode of Transport Recommendation Needed

Hello,

I plan on visiting Sri Lanka, South West Coast majorly. I need some advice/suggestions/recommendations on the mode of transport to be chosen.

I am planning a 10 days trip.
Starting from Colombo to Ahangama, where we will stay for 3 nights and then head to Hiriketiya Beach for another 2-3 nights. Will be covering Mirissa and other beaches around.
Thereafter plan to move to Ella from Hiriketiya Beach directly and stay overnight around Ella for another 3 nights before coming back to stay for 1 overnight in Negombo and then leave Sri Lanka.

I was thinking to experience the Train travel which goes near the seashore on the coastline from Colombo to Ahamgama. Then rent out a Tuk-Tuk for few days to explore nearby areas.

Where I am stuck is the last phase of the journey.
Hiriketiya/Mirissa to Ella and then Ella to Negombo.

I was thinking to do a complete Tuk-Tuk rental for Ahangama - Mirrissa - Hiriketiya - Ella and back to Ahangama. Leave the tuk-tuk there and take a return train to Colombo and go to Negombo.

Please suggest if any other better alternative or option.