Hey, make sure you check out the tide before visiting Sukhumvit.
low tide is good for swimming, surfing stuff cause when it is high tide, people often noctice that when they step into the water they could walk just a few feet and then step off a sandy ledge.
I found this useful site for tide checking https://www.tideschart.com/Thailand/Samut-Prakan/Amphoe-Phra-Samut-Chedi/Bangkok/