Zip sheets

My son is almost 5 and he is waking a lot at night and calling me in to cover him up again (just the sheet in summer). Needless to say we are both a little sleep deprived. He tends to move a lot in his sleep and so his sheet is usually twisted around and around and that’s why he can’t do it himself as he can’t figure the tangle out. I saw the zip sheets and thought maybe they would be helpful but as they are expensive I was hoping that maybe some other mums had used them and could let me know if they are good and if they helped at all. Thanks.