Have you thought about using forms for differentiation? The recent forms branching update makes this possible. The branching logic feature allows you to determine which questions students will be prompted to answer based on their responses. This would be ideal for differentiating your warm-up questions prior to your lesson. For example, you can design the form to branch to more rigorous questions as students answer questions correctly. You can also branch students to less rigorous questions as questions are answered incorrectly.
Learn more about branching features here: Microsoft Branching Updates