Order picking (OP) is a process that occurs in warehouses of unitized goods and it includes all activities that follow the retrieval of demanded goods, according to demanded type and quantity, with the intention of meeting customer demands, accurately and on time, with acceptable costs. As the OP process can contribute up to 50 % to the overall warehouse operational costs, design of the order picking system (OPS) needs special attention during the warehouse design process. In existing systems, the need for improvement is often caused by the change in demands. This paper analyses the possibilities of low-level picker-to-part OPS improvement through appropriate decision making on different design levels: tactical and operational. In this paper, a simulation-analytical model is developed to evaluate different OPS scenarios based on three storage assignment policies, four routing strategies and two different OP methods. Two layout variants and the evaluation of the required workforce are considered as well. The experiment results indicate that the application of the proposed model could lead to significant improvements regarding OPS performances and resource utilization. 35 refs.