I don't understand what the problem is here. Why can't you use the
coil calculator?
Single
coils:
28g, .9ohm: 6/5 wraps on 2mm, 5/4 wraps on 2.5mm, 4/3 wraps on 3mm (not super practical)
26g, .9ohm: 9/8 wraps on 2mm, 8/7 wraps on 2.5mm, 7/6 wraps on 3mm
You wouldn't typically make a ~1 ohm coil with 24g wire, but you could do a 10/9 wrap on 3mm for .9ish ohms.
For duals, just double the wraps. For example, if you want a .9 ohm dual coil with 28g and want the ID to be 2mm, make two coils with 12 wraps instead of one with 6. Each coil in a dual coil set up will be twice the target resistance; i.e. for a 1ohm dual coil, each individual coil should clock in a 2ohms.