I switched to a sit-stand setup two years ago and it did reduce my low back pain, but only after I stopped trying to stand all day. The biggest win was breaking up sitting with regular short standing blocks. I started with 15 to 20 minutes of standing every hour and built up to 30 to 45 minutes at a time, totaling about 3 hours of standing across the day. The novelty wore off, but the pain relief stuck once the habit was consistent and I moved around instead of locking my knees. If you stand still and slump, your back can feel worse. Alternating and micro-moving is what helps.
Get an anti-fatigue mat around 3/4 inch thick, wear supportive shoes, and use a small footrest or even a box to prop one foot and switch sides. Set your monitor so the top is roughly at eye level and the screen about an arm's length away, and keep the keyboard and mouse so your elbows are at 90 to 100 degrees with wrists neutral. A leaning stool or perch lets you offload without fully sitting. I also set a timer for a 30-30 sit-stand rhythm and take a 2 minute walk or hip stretch every couple of hours. If you have radiating leg pain or numbness, get that checked, since a desk change alone will not fix nerve issues.