iirc it dooesent have to cover your ankle unless said in site ppe standards. quite a few people wear i work wear safety boots that go to just below ankle.
Thats safety shoes then not boots
The footwear should be suitable to the job you're doing not the site minimum as highlighted in the risk assessment for the job.
At my site there is many different types of boots I can wear depending on the job am doing. If Im not wearing the correct ppe and I get hurt I wouldn't be aloud on the site again. Same goes for gloves, head protection, eye protection etc Ive got a tool box full of all the different ppe I can wear during the day depending on the jobs am doing.