Draw it 1:1. Draw it at real size.
A complete wood plank will be around 220 cm long, or a bit more than 7 feet max. That is not big deal on a vector based program.
The trick here is to use a vector based program.
Try Illustrator, Corel Draw, Affinity Designer, or the free ones Inkscape and Gravity Designer.
Keep the design in vectors, do not rasterize anything.
For the provider, you probably need to export the design to PDF. Always talk to him to ensure the design is not scaled by him.
Actually, the first step is to know what are the limitations of the printer or plotter the provider is using. If he has a 90cm max width roll of paper, that is your limit for the file. Make for example a file 90x220 cm and ask them to print it at real size.
One additional tip. Draw several scales across the template. Rulers for example of 6 inches or 15 cm here and there, so you can confirm the template is at scale.