I need to build two minimalistic antennas for RX/TX at ~433MHz. I have insulated solid core copper wire, but I need to make it perfectly straight. I was thinking of using the type of sticks you set next to plants to support them while growing but perhaps there is a better, less ugly way. What do you suggest?
Based on the information you have given in the post and comments, the simplest way to construct a "omni" for 433 MHz, is by using an SO239-chassis-connector, and solder/screw the antenna elements directly onto the connector. Make sure the ground-plane elements are bended down, to ensure a close match to 50Ohm impendance.
The single-strand/1mm wire will do nicely without supports.
Here is an example:
The dimensions can of each of the wire elements would be 300/433/4 (a quarter wavelength), each element would be the same length.
Start with somewhat longer elements, and "prune" them until you have the lowest SWR for the intended frequency.
If this is not what you are looking for, please update your post with more information.
To straighten single-conductor copper wire, clamp one end in a vice, grab the other end in a pair of lineman's pliers and turn the pliers so that the wire is wrapped around them a bit. Pull to tighten the wire, then hit the wire-end of the pliers with a hammer (going away from the vice). Easier to do than to describe.