You can also try Wal-Mart or Target or somewhere. You can try a regular thermometer but I don't think it will work. I know I tried it way back when before I started with my BBT & it didn't work for me... just confused the heck out of me. BBTs are extremely sensitive & that's what you need b/c you are looking for a very minute change in temperature... I think 2 degree change, if I'm not mistaken but I could be wrong on that. Whatever it is I know it's small. If you can't find one locally you can order it online. Actually I have ordered online here so I know they are reliable if you want to check them out...
Basal Thermometer - Digital. I don't have THAT particular BBT but I'm sure it is just fine!
Yes you do tend to get into a pattern so you can kinda predict when you will O each month. Another benefit is really just learning your body. You start to really learn when you are fertile so that you can read all the signs correctly the better you get at it & the more you do it. You can also keep up with when you DTD as compared to your temps & that will confirm whether or not your timing was good that cycle.
Oh I also wanted to add you should take your BBT first thing in the morning upon waking up & after I believe at least 3 hours of sleep & before doing literally ANYTHING, including running to the bathroom to pee.