The wooden walkway I have in mind is on the southern end of Samae Beach, on google maps "Wooden Walkway" and "เนินชมวิวหาดแสม ".

Canoe with clear bottom would work, but I just went for swimming in the sea (at night 10 pm, at a place with the least possible artificial light) and that is cheaper and independent from the boat service provider. I just checked South Pattaya Beach: plenty of fluorescent plankton, you just can't see it there on the beach.

There is a google maps entry "Koh Larn Garbage Dump บ่อขยะเกาะล้าน" which was the highlight of my last trip to Koh Larn (about 5 years ago, at that time I didn't know about fluorescent plankton).