Nice fabrics ...
Hi there Twiggy and welcome to TSP ..
Do you want it to be a 'manly' quilt ??? or not too bothered ?
You could do something like
this (found in the Tutorial section of The Darkside) from the centre point of each 'cobblestone' or even from the intersection of four seams.
This would of course break up the pattern, which is something you may not want to do having taken so much effort to make it ...
Another idea would be a diagonal line from each of the eight outer corners of the cobblestone ... which would make a nice 'star' effect ??!! Mark the middle point with a ruler and aim for that point with each line, continuing through to the opposite corner ... I quite like that idea but then straight line quilting is very much my thing.
Failing that diagonal crosses are very effective, but I dont know how big the cobblestones are ... if they really big you will need more than that ... an outstretched hand placed on the quilt should touch lines of quilting ... thats the general rule.
Im another one who steers clear of SID; its a bugger to get right, takes time and you cant see the stitches in the end if you do get it right ... so a lot of effort for not much reward other than a held together quilt.