As ghellquist commented, this depends so much on the musical setting that it's impossible to answer confidently without further information.
However I'm going to disagree with Todd Wilcox. Using in-ears is, more often than not, a good idea, and they don't need to be overly expensive – provided you're ok with being cable-bound. Cheap wireless systems will only give you lots of noise problems, incontrollable dynamic-range issues, drop-outs at the Sod spots... Cable-bound headphone amps are cheap and reliable though.
The in-ears themselves should be decent quality (positively don't use consumer in-ear headphones!), but that doesn't mean you need crazy top-notch 4-way systems that cost thousands. The lower-range models e.g. by Shure, albethey not super comfortable and not exactly nice-sounding, can still allow you to hear much better that with the typical floor monitoring system.
The mix is is important, but this is doable. Requirement is of course that you actually have an aux channel at your disposal; fortunately, these days digital consoles with plenty of them start to become the universal norm. The general guideline with monitoring in general and also with in-ear is: as little as possible. When I set up a new mix for my in-ears, I start out with only my own signal and the most important signals I need for orientation (playing bass/cello, this is generally keyboards, rhythm guitar and a bit of kick drum). I set up the volume of these so I can still hear everything else about ok through the direct sound from the other musicians' instruments / floor monitors. Only when the crucial elements are fine, I consider whether I need a bit extra of some of the other instruments.
The most important thing you actually need to get used to is how in-ears change the way your own voice sounds. That's a main factor why more expensive models, and custom molds, are desirable. If you only sing harmonies then this isn't so much of an issue (in fact, the strong amplification of the inner voice can be useful), but for lead vocals this can be quite weird at least at first.