Blue Yeti is an excellent USB mic for a PC which has USB jacks. However, if you are going to stick with your iPhone or iPad, you need to buy a lightning-to-USB adaptor and may run into some unnecessary trouble. If I were you, I would find a mic designed for iOS, such as Shure MV88, $149. There are a few of them on the market. Just Google "mic for iOS and find something within your budget.
If you prefer to an economical route, a lav mic with lightning connector will do a decent job. You can find one under $30.
