BBT thermometer Question

Deandra • Angel baby lost 06/13. Baby gone 05/13/2016.

Hi ladies, I've got a question. Excuse while I ramble! Haha

My fiance and I arnt TTC but are also not taking serious steps to avoid it. Basically no sex on peak ovulation days and pulling out. We're not trying yet but after 6 years together and one miscarriage a baby wouldn't be a bad thing.

I've noticed these last few months that Glow has been estimating my periods arrival 2-3 days before it comes. I chart my CM and am learning my CP but I was wondering if I charted my BBT if my calendar would be more accurate. Since we arn't TTC i'd like to get as close an estimation on my ovulation dates as possible. Now for my question.

Can I use a regular thermometer or should I buy a BBT thermometer? What's the advantages?