What is the best serum to use with microneedling for firming the skin on the body?

The three most commonly used basic serums for microneedling are vitamin C serum, Hyaluronic acid, and platelet-rich plasma or PRP.  PRP is a portion your own blood and is best used for hair restoration.  Vitamin C serums can be helpful for color correction or evening skin pigment.  The best serum for general microneedling would be a hyaluronic acid serum.  Hyaluronic acid is one of the components in collagen.  By using a hyaluronic acid serum for microneedling you are directly providing the skin the building blocks for making new collagen.
I would recommend using a dermal roller with needles no longer than 0.5mm.  Deeper treatments should be done in an office setting with topical anesthesia.
Good luck, Dr. Z 

Can not recommend you any cheap brands as we use medical grade copper peptides. The most important aspect is skin care to reduce chances of infection but also skin colour changes. Use a bland moisturiser like aqueous area or white soft paraffin- these area as cheap as they get. Also sunscreen use is vvvvvv important, especially if you live in Asia. The use of SPF is essential. Wait 3 days before skin heals, use hats, and sunscreen twice a day. All the best, Dr Davin Lim. Brisbane. Australia.