For me, the compostela is only a piece of paper with some nice colours on it, but it is still on display in my home! In terms of shorter caminos - I walked the Ingles from Ferrol to Santiago, which was much quieter from the Frances, and that was a combination of trail and smaller farm roads without too much walking near big roads and so forth, although you do encounter them from time to time. As a smaller camino though, even in September last year the accommodation was quite busy, but with two of you finding cheap rooms shouldn't be too much of a problem.
After Sarria, the last 100km does get quite busy - I've only walked from Leon on the Frances, so can't comment on the earlier parts - but in terms of path walking I think that maybe Astorga over the Cruz de Ferro was quite good with minimal paths, and I might then go on to cross O Cebreiro as well - but I do like climbing and ascending rather than flat walking, so it may be a matter of preference. Keep researching, and I'm sure you'll find something that ticks a fair few boxes for you.