Buckle initiation devices, such as sleepers and distributed buoyancy modules, are typically adopted to initiate lateral buckles at pre-determined locations to release thermal expansion in a controlled manner to ensure pipeline integrity. For pipelines installed by S-lay, sleepers are desired as it is difficult for buoyancy modules to pass over the stinger rollers. If the thermal cyclic fatigue is critical in the pipeline design, pipeline lateral buckling designs may result in small sleeper spacing. As such, buckle reliability of conventional sleepers may be inadequate in some cases. In this paper, lateral buckling mitigation with sleepers is investigated using finite element (FE) models for a water injection pipeline. Sensitivity analyses are performed on key input parameters including single and dual sleepers, lower bound and upper bound friction factors between sleeper and pipeline, berm effects on soil lateral resistances, and sleeper heights. Based on the sensitivity study results, a mitigation solution combining sleepers and mattresses under the pipeline touch down zones is proposed and evaluated. It is found that sleepers combined with reduced touch down point lateral friction can reduce the maximum longitudinal strain and thermal fatigue damage by more than 50% as compared to using sleepers alone as mitigation. Therefore, this design adds a new option to allow increases in the sleeper spacing and improved reliability of buckle initiation.