Hi @HelpBrock,
A warm welcome to the Bunnings Workshop community and thank you for your question.
The only self-levelling compound that I am aware of that can be used over timber subfloors is this Dunlop 15.9kg Timber Floor Level Flex Kit. It contains both a primer and a levelling compound. It can be applied directly to the timber subfloor for levelling, then a layer of plywood 6-12mm thick should be applied over the top before your finished flooring. Considering the need for plywood over the top of the leveller, it is going to be best to remove the skirting and reinstall it after the project is complete.
Can I trouble you to upload some photos of your place? Seeing what you're working with will certainly help our members understand what you are dealing with. Let me know if you need a hand with this, I am happy to help if required.
Unless the holes in the flooring are deep enough to punch through to the other side of the flooring, then there is likely no need to fill them, as the self-leveller would do this when it is poured. If there are particularly concerning holes, then filling them with wood filler would certainly be worthwhile. Around the perimeter of the room, it is worth filling gaps to stop the self-leveller escaping sideways. This can be done with a caulk product such as No More Gaps.
Unless you need to apply an incredible amount of this product, in which case I would recommend other methods to level your floor, then you won't have any real issues with weight. If you have concerns based on the condition of your home, it is worth contacting an engineer for their assessment before continuing.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
