Hi Jelyn,
How are you?
With regards to your situation, you can still apply for an FLR(M) with the amount of time your visa has left. You don't have to apply spousal visa since you are already here in England...you will only apply for a a spousal visa if you are outside the UK. What I'm saying is, instead of spousal visa, you do need to apply for an FLR(M) or Further leave to Remain "Marriage" after you got married. It is more likely the same as spousal visa.
You don't have plenty of time though since your visa will runs out on October and you're getting married on August...my suggestion is, as early as possible, gather all the requirements for the FLR(M) application so after the wedding you could immediately submit your requirements to the UKBA. If you do that, you will be fine.