I would suggest a simple cow call for one, I use the Primos Cow Girl call
https://shop.primos.com/pc-897-15-cow-girl.aspx

Another good call would be the Hoochie Mama, which is simple to use as well.
https://shop.primos.com/pc-571-15-hoochie-mama.aspx

Course don't forget a decent bugle call...don't want to sound like the "King of the Mountain" so I use the Primos Pack Bugle
https://shop.primos.com/pc-571-15-hoochie-mama.aspx

If I could suggest, watch alot of videos and listen to the calling techinque of the callers in the background. Kinda hard to focus on it when a big bull is on the tube, but it will help you. Don't be afraid to call along with them to copy the sound.

Good Luck