The bags of "mulch" you buy in stores are NOT the same as wood chips. Wood chips include the center section of the tree, which is "old growth". This is the part that is very slow to break down.

Typically the mulch in the big bag stores are BARK mulch. This breaks down much quicker, and won't leach nitrogen from your soil.

Honestly, the wood chips on the top of your soil won't leach nitrogen either. It might impact the very top layer of the soil, but not the root zone. The impact of wood chips only matters if you AMEND the soil with wood chips.

Wood chips have their place in the garden though. They make for great paths and areas around your beds, specifically BECAUSE they break down slower and will not need to be replaced as often.

Good luck and a great sunny location for your garden! I hope this helps.