I have a lot of relevant experience, trust me. I can make this real simple for you. You only really need one product - polyethylene glycol 3350. In the U.S. it is called Miralax. You mentioned Movicol Laxido, which is another brand of the same stuff. It's a white powder you stir into a beverage. There are a few generic versions - all exactly the same stuff. Big difference in price. This product is both a stool softener and a laxative. If you take enough of it, you don't need anything else.
It is an "osmotic" laxative. That means it works by pulling water into the fecal matter and holding it there. This is exactly what fiber does. I would caution you to avoid "stimulant" laxatives, like senna. Stimulant laxatives work by irritating the nerves in the lining of the colon. I'm not a fan of irritating delicate body tissues. It's unnecessary. Stick with osmotic laxatives. The stuff is a bit pricey. If you can't afford it, good old milk-of-magnesia is also an osmotic agent, and it's real cheap. (Some heart patients need to avoid taking in too much magnesium. That's a rare condition. Also, some kidney disorders make it necessary to avoid magnesium. Again, that's uncommon. Most people don't consume enough magnesium.)
I learned all this because I developed severe diverticulitis. I was facing possibly having a portion of my colon removed. With that condition, the most important thing is to make absolutely sure you poop every single day. After a lifetime of chronic constipation, I finally got religion when it came to good bowel hygiene. I take a scoop of polyethylene glycol in hot chocolate every morning. Once in a while I skip a day. Now and then, I take multiple doses in one day. Your body will let you know.
MYTHS: when it comes to bowel hygiene, there's a lot of wrong thinking out there. Doctors tend to not give the best advice, even gastroenterology specialists. So: osmotic laxatives are NOT habit forming. You don't get "addicted" to them. Stimulant laxatives can create dependency, as the bowel gets used to being over-stimulated. (Actually, that has been up for debate lately.)
TRUTH: Constipation causes a build up of pressure in the colon that can lead to diverticulitis, which can further lead to some really awful things. We need to poop every damn day, come what may. Take an "osmotic" laxative as often as needed to make that happen. Your goal is to pass stool that is formed, but not hard. It shouldn't hurt to poop.
Fluid is fluid. Anything wet has water in it. There is no need to be sucking down gallons of water everyday. All you have to do is monitor the color of your urine. It should be light yellow (like real lemonade.) If it is colorless, then you are drinking more than enough . . . and possibly flushing too much salt out of your bloodstream. Excess fluid intake can cause seizures, as Brooke Shields found out. Also, heavy fluid intake can be a burden on the heart, causing fluid to back up into the lungs. On the other hand, if urine gets dark yellow or orange, then start drinking more. Good bowel function does require that you be well hydrated.
