I use these currently and they work perfectly...i like to do stuff outside though on trees so if you are planning to use them outside when you're "on the go" i'd get a set of these

https://www.amazon.com/Nayoya-Gymnastic-Strength-Muscular-Bodyweight/dp/B009RA6C1K/ref=lp_3203160011_1_2?srs=3203160011&ie=UTF8&qid=1507391112&sr=8-2