I'm writing a blog post at the moment on timing. If you shag regularly and don't have really long cycles it's not necessary to track your cycle. If you tend to be a bit haphazard or lopsided with when you DTD - say you do it loads around when you think you're fertile but not so much otherwise - and you've been trying a few months without success then it's worth looking at.
Very normal to ovulate on different cycle days month to month. Your luteal phase (ovulation to period) should stay the same. But be careful you're counting cycle day 1 correctly, as spotting can be confused for CD1 and that can mess up your luteal phase calculations. CD1 is the first day you need to use some kind of sanitary protection.
Temping is best for confirming what your ovulation date actually was especially when combined with cervical mucous observation. OPKs are better if you want something to tell you you're fertile NOW, go. Personally I don't use OPKs but have been temping for around a year now and after a few months I could tell from my temps/CM when I'm in the fertile week even when I haven't hit ovulation yet. Combining OPKs with temping is also useful if you want even more info.
It is a bit of a myth that temping is some hugely difficult and delicate thing. You can do it just fine with a cheap thermometer, you don't have to wake up at the same time every day, and if you forget a day or two you will still tend to see an overall pattern. Of course the more you stick to the proper rules the more accurate it will be, but I'm really haphazard with mine, and it still works.
This last one I'm not 100% sure - but I think that your own natural fluids are more friendly to sperm than the special lubes, and the lubes are designed for women who don't get as much fluid naturally. So there's a possibility it could do harm by overwhelming your natural fluids? Maybe worth trying one month with, one without and alternating.