The fact that you want to build a queen instead of a king makes things a bit more complicated (precut split layers really only come in twin XL). Good news is at least you know what it would entail to be successful and then you can decide the best way to proceed given your specific situation. Alot of folks start down the DIY road without understanding what’s really involved and whether they are actually up to the task of seeing it through. Where I am up in Canada I litterally could not buy a prebuilt mattress that worked for me so DIY was really my only choice (perhaps unlimited budget I may have found something good enough eventually). I also had to increase my budget quite a bit more than I originally expected but after litterally getting injured sleeping (never would have thought that was even possible) I was determined to solve the problem once and for all. Very happy I went that route myself but again it’'s not for everyone and it’s also good to know your own limitations.
Here’s my build thread which you may find useful as well:
https://forum.mattressunderground.com/t/simmons-beautyrest-mattress-rebuild