I know exactly what you mean... boucle can be stubborn to unravel....
For carrying a yarn up the side while it is not in use, I will do my best to describe how I do it... first, let me say, that I do this in instances when I don't have real far to carry it. For example, of the color was used only at the naval, and then not again until the neck, I wouldn't carry it up all those rows; I would just end that yarn and rejoin it when it was needed much later. But at times, when doing a striping pattern, you just need to carry an unused yarn a couple rows and then you will be using that color again.
So... here I go trying to explain...
When you are done using Color A, at the end of the row, join Color B (you are going to start working with Color B, and 'carry' Color A up the side edge until it is needed again).
Once you join Color B, take the strand and 'twist' it with the color A before you start knitting with the Color B. You are just twisting the two strands of each color together, I just make one twist, to 'connect' them, shall we say. And that one twist will bring the unused color 'up' even with the new row of knitting. Then, you knit across and back with Color B that was just joined.
Now that you are back where Color A is hanging, if you are ready to use Color A, twist it with Color B, drop Color B and pick up Color A... knit across and back. However, if you are not yet ready to return to Color A, then still twist the strand of Color A with the strand of Color B again, to bring the unused color up even with the new row of knitting, and then continue across and back the row with Color B.
The 'twists' are just one yarn twisted once around the other yarn, and I like to always do it the same way (Color A over Color B or vice versa), and remember that this will be hidden when you sew the seams of your sweater.
This action of simply making a quick twist of the two yarns will allow the 'carried' color to neatly follow up the sides of the rows, and be ready for when it is to be used again. Bear in mind that if you are doing flat knitting, wherever you 'dropped/twisted' the color to be carried, that is where it will be available to be picked up again. So for example, you could do 2 rows of color A, then do 2 rows of color B and so on. However, you could not do 3 rows of color A and then switch to color B, because it would be at the opposite end of your knitting.