Best soil amendments for blueberries

My blueberries are planted but I tested my soil (using the at home method with vinegar and baking soda) and it seems like my soil is slightly alkaline. What are the best ways to lower the PH? I bought soil acidifier but I read that was a short term fix. Based on my Google searches it doesn't seem like pine mulch or needles effectively lowers it. Sulfur is good but only before you plant. Wondering what my best course of action is.