Documents required to get married

It's highly doubtful that you'll be able to proceed without your birth certificate.   Do your British naturalization papers show your mother's and father's full names?  This is important information to Brazilian registry offices, so if that information is on your naturalization, the cartório MIGHT be persuaded to accept it in lieu of a birth certificate.
Bangladesh has an honorary consul in Moema, and its embassy in Brasília; they may be able to help with the birth certificate.
You may consider speaking with an attorney; if s/he seems doubtful of success,  that route probably isn't worth pursuing.
If all else fails, you and your fiancée still have the option of going to the UK, marrying there, registering your marriage at the Brazilian Consulate nearest your home, and registering the Consular "Certidão" of your marriage at the cartório when you return to Brazil.

Hi thanks for replying so my parents names are not on the naturalisation papers and I think it will be very hard for us to get married in England because I have to be working and earning over a ceirtain amount I think 18600 after tax to apply for her to come over, I have been looking for an email to contact the Bangladeshi embassy in São Paulo but none of the emails I found online work also at the moment I am very low on cash and earning cash by giving lessons on skype, because when I came here I had no intention of going back to England because I don't have any savings, a job or anywhere to live there. I have my Bangladeshi birth certificate and it does show my parents names on it do you think there is a possibility that it could be accepted without having to be legalised at the Brazilian embassy in Bangladesh? also do you have the address for the Bangladeshi embassy in moema please?

It's not an embassy, it's a consulate.  The embassy is in Brasília.
Google "Bangladesh Consulate São Paulo", and you'll see the complete contact information.

You must have a Birth cert with parents names on it, it must not be older than 90 days and must have an Apostile. Once you have these you can have them translated in Brazil.(cheaper)
While I was in Brazil I was able to get these documents online (New Zealand) and have them emailed to me. Maybe check online if your birth country can do the same?
Once you have a Brazilian marriage cert, getting residency is very easy to do.

I forgot to mention you also need a Certificate Of Non Impediment also with an Apostile and no older than 90 days.
( to say you are not currently married)

StaceNZ wrote:

You must have a Birth cert with parents names on it, it must not be older than 90 days and must have an Apostile. Once you have these you can have them translated in Brazil.(cheaper)
While I was in Brazil I was able to get these documents online (New Zealand) and have them emailed to me. Maybe check online if your birth country can do the same?
Once you have a Brazilian marriage cert, getting residency is very easy to do.

Is the apostilled birth certificate again needed in the residency (or even citizenship) application?

Good question, i also wondered at the time but No you will only need your birth cert for marriage. Once you get your marriage certificate it will have your date of birth and parents names on it.

StaceNZ wrote:

Good question, i also wondered at the time but No you will only need your birth cert for marriage. Once you get your marriage certificate it will have your date of birth and parents names on it.

Is the place of birth included in the marriage certificate?