Flowers and chocolates should be given on Teacher's Day, but anti-fatigue bracelets can be given to boys. Teachers are very hard-working. There are so many national regulations now. Students who are disobedient must be educated by language. They cannot be beaten or scolded. Some students are just against teachers. Teachers are the hardest profession. Although the effect of giving him an anti-fatigue bracelet is not immediate, it will have some effect in a subtle way. For the sake of your boyfriend's health, giving this gift will also move him.
When a teacher's clothes are usually very particular, he should be a role model. You can give him a few better clothes, which must be comfortable, so that he will be more comfortable when teaching. Razors, belts, wallets, etc. are necessities in life, and it is also appropriate to buy them for him.
I think the most important thing is your own intention. If you choose a gift for him with your heart, he will definitely understand the importance of this gift and your intention.