Two Proprietorship firm one has GST second doesn't

I am running a proprietorship firm registered under my individual PAN and no GST number because turnover is under limit . Now I am planning to start Trading firm ( proprietorship) for which I have to take GST Number otherwise I will not get Input credit . My question is if I take GST number for second firm, will it applicable to first firm also because of single PAN ? Will I have to submit GST return for both firms? or only second firm GST Return will be sufficient? OR I should go for PARTNERSHIP Firm for second firm to keep it separate.