I have created an H-bridge PC with 4x floating gate drivers and 4x IGBTs (see attached schematic showing half of h-bridge).

It works very nicely but I would like to replace the IGBTs with n-channel MOSFETs. However, all the H-bridge designs I've seen use n-channels on the low side and p-channels on the high side.

Since my design uses independant galvanically isolated DC-DC converters which effectively provide each of the 4x gate drivers with their own floating supply, is it possible that I can just do a simple straight swap between of the IGBTs with N-channel mosfets?

 

Sure, why not?

You'll get better gate charge/discharge times if you reduce your DC-DC converters to around 11v-12v.

Make sure that you leave enough "dead time" for the MOSFETs you're going to use. MOSFETs usually turn ON faster than they turn OFF. Failure to provide enough dead time usually results in smoke.