Wah, congrats on your pregnancy! Honestly banyak of us did the Sinovac-then-Pfizer booster route, and generally boleh je lah, just make sure you inform the nurse yang you're pregnant so they can note it down, especially since you're already 25 weeks. Some of my mum friends said they got a bit of arm soreness or slight fever after the Pfizer booster, but nothing serious, and most doctors are okay with it during second or third trimester. Best to check with your gynae first though, as they'll advise based on your specific situation, but don't worry, many preggy mums have done it without issues!