Thanks again Tabitha. Yes, my wrist is 15.5cm too and I generally don't like bracelets to be too close fitting, but I am planning to build this bracelet over the longer term and don't want to risk losing it etc.
I'd love to try a full bracelet in both sizes but my local Pandora doesn't seem to have any on display! They are all half full at best. Have to go into Oxford St to see if I can find one.
I am also planning for 3 muranos so it's good to know that the 19cm fits you well as your wrist is the same size as mine. I have an oxidised one now too, and it's 18cm, but it only has the clips and one charm and therefore fits well. I could imagine it being fine with the muranos only if it did stretch a little.
I have to take some new pics when I can...
Once again

for your advice, as always