I just support mine on jackstands by the rocker panels when I separate subframe from body. A couple small strips of lumber...like foot-long cut strips of 3/4" plywood...laid on each side of the pinch weld, will distribute weight along the rocker and prevent any damage to the pinch welds. The location of support will gives you full access to replace the floor and to reach all the subframe bolts.

Remember a body without an engine/trans, subframe, suspension, interior, etc is very light in weight...so there is little fear of doing any damage to anything if you're just basically supporting the weight of the firewall and floors...and dash and doors if still attached. So you can pretty well use any solid bit of metal that you won't be cutting out to support the front of the unibody.

Frankly it will be light enough in weight that your biggest concern really needs to be avoiding leaning/pushing/beating hard enough on the body while working on it that it starts to shift on your supports and possibly fall off of them. When doing such work I take extra steps to actually attach the top of each jack stand to the chassis. All kinds of creative ways to do this...screws/bolts/u-bolts/lumber, tie them together with wire, even tack the car and jackstand together with a welder or whatever...but with some method I just set it up so that in the unlikely (but possible) event the body of car gets forcefully shoved any direction, I want the jackstand to harmlessly slide on the floor along with the body, and NOT the body to slide relative to the top of the jackstand...which could cause serious damage/injury/death.

Such unwanted movement is ESPECIALLY easy/risky if you still have the rear axle in the car and the rear tires are free to roll...allowing the car to pivot. If this is the case also use FOUR very solid wheel chocks on the rear wheels. I'm not sure how far you're disassembling the car, or how high you intend to raise it up in the air for whatever you're doing here...