When I have bobbin issues, first thing I do is take it out, look for loose threads and "dust balls". I clean it all out, oil if needed. Then I move on to make sure the bobbin is wound right. Sometimes bobbins get wound to loose and can cause problems, or if they're close to being emptied they can get a little weird. Once all that's done I recheck my tension and reload the bobbin. Usually before I actually quilt on my quilt I make a practice sandwich and test out my tension and threads on it. Then when I'm happy I go to my actual quilt.
As for thread suggestion, sometimes when the pattern has a lot going on, I opt for clear thread. It doesn't detract from the design. It can be a bit tricky to work with though. A varigated thread might be the way to go. Either a grey or brown. Would love to see it on here when it's finished!!