I would recommend the cheap ones on Ebay/Amazon. You can get 30odd for a couple of pound.
Do you know roughly when you ovulate? It can vary every month. I would suggest starting on cycle day 8 and test twice a day (or like me, every hour lol). It's not recommended to use first morning urine, so test mid morning and then mid afternoon perhaps.
Some ladies surges are over quite quickly, but I have positives for two days running. If you check frequently you shouldn't miss it.
Once you've been testing a couple of months you may be able to narrow down testing days as well.
And personally I would have sex when you get a positive, and for several days after (and to the run up to the positive if possible!). Actual ovulation should occur 12-36 hours after you get a positive OPK (unfortunately, if you get a couple days of positives like me, pin pointing ovulation proves a bit difficult)