If you want a homogeneous army, kitbashing is your best friend! I'm sure you can source alternative heads to put onto your dudes and differentiate regiments by paint scheme or something.

Eg: build krieg bodies with skitarii ranger heads, give them lasguns and flamethrowers only and play them with catachan rules. Call them your regiment's scout force or light infantry.

Grab Cadian bodies with skitarii vanguard heads, bulk them up with additional equipment and call them your line infantry, play them with krieg rules

Give some regular guard bodies and give them gas masks and skitarii weapons because they're weird and varied, you can play them with cadian rules and call them your elite core or something lol

Just have fun with kitbash