@MartynRich - Yip you are a very talented songwriter, most DAW's have the feature to add tempo increases/decreases, it just takes a bit of reading and practise. I recommend copying the otriginal song to a seperate "try it out" version and invest a few days in nailing the feature.
There are two approaches, record it and then speed it up, or determine ine the tempo chnages and then record over that, with the latter method, the metronome will speed up to make it a bit easier to follow...however it might not be easy to make it sound convincing, however you do it..
With the first approach (above) there will be considerations like if you speed up audio tracks then you won't wont it to chnge the pitch to a higher note, In Studio One it can handle this, if you have Zanaptiq timestretch inbuilt it will keep the pitch constant. Try and keep as much in the MIDI realm as possible, which will be hard if it's vox and guitars.
Hope this helps.
R