Looking for input on hardie fascia and what material to use to replace existing

Currently my home has the old pressboard almost like cardboard fascia. It's getting soft in several locations. I want to replace my fascia along with my soffit with hardie. The problem is the only Hardie material I have found in the 6" is 3/4" thick. My exiting pressboard stuff is like maybe 5/16". The pressboard is attached to 1x6. I'm afraid if I remove the pressboard and try to replace it with the 3/4" thick hardie it will not fit under my existing drip edge. Do they sell a hardie material that is thinner than 3/4" for fascia? I found a 6.5" lap siding that is about the same thickness as my existing fascia. Could I use that? Can I just attach the hardie directly over the 1x6 after removing the old fascia material? What nails should I use to attach the hardie fascia and soffit? I installed some 4x8 hardie soffit under my entry way at my front door and tried to use some of the screws Homedepot sells for the hardie and that was a joke they were way too thick. I ended up just using ring shank nails.