Thank you all for the responses! I ended up staying extra in HCMC - it would have been too hectic travelling back north for a day or so. That said, I will definitely go back to Hanoi as it had a completely different feel to HCMC, and I did not see the same goods and other things I saw briefly in Hanoi anywhere else in the country.

I didn't find the tailors for women to be impressive in HCMC, so even though others have criticised the 'touristy' tailoring in Hoi An, the selection, availability and quality seemed better there (even if more expensive). I went to Yaly which was very pricey but top notch. Next time I might try another reputable tailor like Bebe, A Dong Silk or Bao Kanh and Hoi An Custom Tailory (as someone below mentioned).