The baking soda helps more with burning and cramping. What really helps me with endurance is the Acetyl-L-Carnitine and a high phosphorus diet. Because our muscles are firing constantly, even at rest, we have a much higher requirement for ATP than a normal person. I haven't noticed any benefit from creatine.
We had a product in the US called Phos Fuel that was just sodium phosphate, but I haven't seen it for a while. Most endurance supplements contain potassium as well as glycine and glutamic acid. All of them worsen myotonia for me. My nephrologist said that skim milk is the best for me to keep up phosphorus levels.
It's important not to use too much bicarbonate. I only put about 1/8 tsp (about 1/2 ml) in a liter of water. Something else that might help is a little magnesium. Again, a lot is not good, but smaller amounts (200-500mg per day) can reduce lactate levels and improve endurance. The best form is magnesium citrate.