If you leave work voluntarily you would be entitled to contributions based JSA for 6 months, and that's it. And that wouldn't start straight away. As you are able to work with your health condition but chose not too you wouldn't be eligible for sickness related benefits, and you may not be entitled to maternity allowance.
Google 'entitled to' and a benefits calculator will come up - this will give you an indication of what you could be entitled to, but remember that voluntarily quitting work would reduce these entitlements massively.
Unless you have a lot in savings or you can afford to live solely on your partners wage (if you have a partner) then I wouldn't do it.
I understand that pregnancy and type 1 diabetes is hard - my best friend has just finished work for mat leave last week - she's having a caesarean next week at 37 weeks exactly and has type 1 diabetes. Another type 1 friend is pregnant with her second, she's worked full time with both pregnancies, she reduced her hours towards the end with both, it worked well for her - she's a senior manager in the NHS so lots of stress!
Could you reduce your hours, e.g. work part time, or use annual leave to take a day off a week? Could you ask to be put on light duties for health purposes? If you declared yourself as 'disabled' when you got your job they aren't legally allowed to discriminate against you due to issues relating to your illness, and similarly with pregnancy, so I'd stick it out. You can go on mat leave 11 weeks before your due date so you could go on mat leave at 28 weeks, which if you are a month pregnant is only 24 weeks away - if you have 24 days annual leave you could take a day a week off?
Also, you are only a month pregnant, a lot can happen between now and the 'safe zone' if you hand your notice in and then miscarry (hopefully not but it's a reality) you won't be pregnant and will be unemployed.