Connecting Threads has great 100% long staple cotton thread in skads of colors. $2.49 for a 1200 yd. spool. Neutrals in 5,000 yd. cones for $9.99. Goes on sale often & also comes in sets for a reduced per spool price. Have you had your machine cleaned? If not, perhaps it's time & ask them to check the timing. If the needle isn't going down at the right time, it won't engage the bobbin thread or will break or your needle will break - often.