Putting a floor into an aluminium boat isn't as complicated as it might seem at first. The floor itself mirrors the bottom of the boat. The floor needs to be supported by small lumber. The supports should run from one side of the boat to the other and be placed every few feet to keep the floor from sinking when you step on it. It can be covered with vinyl, carpet or any other floor covering you can imagine. The floor that's not in direct contact with the bottom of your boat doesn't carry sound and is easier on the feet than the aluminium hull.
Use a measuring tape to measure the length and width of your boat's bottom. Multiply those two dimensions together with a calculator to determine the number of square feet of marine plywood you will need for the floor.
Measure the width of the bottom of the boat at the very back, the very front, then every 2 feet in between those two. Record each measurement and use the jigsaw to cut the 1-by-1 lumber to these lengths. As you measure each piece of 1-by-1, mark the centre of each piece with a pencil.
If your boat requires more than 1 sheet of plywood, butt the pieces of plywood together. Lay the 1-by-1s on top of the marine plywood parallel to each other and 2 feet apart, so that the marks at the centres of the 1-by-1s form a straight line. Use a pencil to draw a line on the marine plywood that connects the ends of the 1-by-1s on the right side and another connecting the ends of the 1-by-1s on the left side. Move the 1-by-1s and draw lines that connect the ends of the left side line and the right side line, as if you're drawing an overhead view of your boat's bottom.
Use the jigsaw to cut along the lines on the marine plywood, making the floor panel(s).
Use marine adhesive to glue the 1-by-1s across the bottom of the marine plywood, as supports and sound isolators for the floor. Use a screwdriver to drive the screws through the plywood into the 1-by-1s. Set the plywood, with the 1-by-1 supports on the bottom, into your boat. Attach vinyl cove moulding to the edges of the floor with screws to keep water from getting underneath the flooring an leaving a mess, or to keep small things, like your car keys, from landing under the flooring.
If you decide to glue vinyl flooring or carpet down to the plywood, use marine adhesive, not the regular vinyl or carpet adhesive. Those adhesives aren't designed for use in the wet environment aboard a boat. After your boating trip is finished, take the floors out of the boat so that the space underneath doesn't stay wet and get mouldy.
This project is simple, but the tools you'll be working with can cause complicated injuries. Keep that in mind and use precautions like gloves and safety glasses as they're needed.