Most mums I know start their maternity leave around week 36 to 38, depending on how they're feeling and what their company allows. I'd suggest checking your employment contract first to see what your entitlement is, then have a casual chat with your manager about when you're planning to go off - frame it as "I'm thinking of starting my maternity leave from [date], is that alright with you?" rather than asking permission, since it's your right. Some workplaces are flexible about it, while others have their own policies, so it's good to clarify early so there's no confusion on both sides.
If I’m not mistaken, HL is usually given only if you have certain conditions and requires “hospitalisation”, whether in a hospital or home. If not, no HL will be given. Also, depending on your company policy, some companies do not recognise HL right before maternity and will need you to start maternity leave instead of the HL if you want to rest before you deliver. Think it is better to check with your company policy and gynae about it.