Firstly, it’s a total waste of time trying Ellesmere due to water conditions being filthy and most areas toxic.
Best accessible area to try is off Rockinghorse Rd southshore where most of the cul-de-sacs have easy access onto the estuary.
Incoming tide, calm night, great fun though I have not done it for years now (don’t actually like flatties anyway).
Go down for a reccy at low tide and spot the channels and troughs (a handheld gps is excellent for marking those)before trying to do the high tide excursion.
Another awesome challenge is using a micro spin rod and reel, a size 10 to 14 fly hook and sea worms found at low tide in the stony area on the Main Rd side of the estuary before you get to the causeway (just past the yachting club).
Take a garden fork with you and dig like mad until you spot them but be prepared for a wee nip, they get pissed off when disturbed BUT Flounders love them!
Just slip the hook into the worm where you expect or know flatties to be and plop the bait out, no weight, no float, but plenty of concentration and be ready for a rapid takeoff!
Re waders, I might be able to help you on some neoprene 10’s, try contacting Ben on 022 1522075.
Green and 5mm I think, very warm. Not sure if he still has them available but very good waders.