Network slicing allows leveraging virtualization techniques for the creation of multiple, logically-isolated network instances over a shared infrastructure. In general, it is composed of a set of unique network functions with a specific physical capacity request. In order to improve network and service robustness, ETSI has introduced the concept of Network Function Set where network functions are replicated and deployed in different physical nodes. In this paper, we integrate this concept of the network function set to implement load-balancing and efficient resource distribution in 5G networks by leveraging on an existing network slice design formulation without the network function set. This helps relieve the burden on the nodes and links and prevent QoS degradation, in particular during failures. We describe how the baseline approach is impacted for the placement of network functions. We then show that our approach improves load balancing and latency with respect to the baseline solution.