[Closed] What wood treatment for a greenhouse?

We have a wooden framed greenhouse that was here when we moved in. It's great for growing etc. but the wood needs some treatment to keep it in good nick.
Previously I gave the outside a couple of coats of decking oil when doing the decking. Now the inside need doing as well.
Is decking oil likely to be the best thing or is some kind of 'wood stain' better? The frame seems to made of hardwood although the panels around the bottom foot of so below the glass may be softwood.
Thanks for any knowledge on this.