Try some texture
Place a textured sheet (such as flannelette) beneath your fitted sheet to create friction between the mattress and sheets.
Add a mattress topper
An alternative is to add a mattress pad or topper to add friction – and as a bonus, they provide extra cushioning!
Non-slip rug grips
Use the matting that keeps your rugs from slipping, under your sheet at each corner.
Safety pins
Secure your sheets to the mattress with safety pins – they will have to be large enough to go through the mattress fabric and the sheet without popping open (and make sure the pins lay flat to avoid them coming undone during the night).
DIY sheet straps
Craft your own sheet straps using stretchy bands and safety pins – or use sew on hook-and-loop (Velcro) to make the straps.
Sheet grippers
These elastic straps are readily available at most retailers and attach to the corners of your mattress and secure your fitted sheet in place.
Attach them in a criss-cross formation for an even snugger fit!
Double sided tape
As a fast DIY solution, try double sided sticky tape. This could be an interim solution until you find something a bit longer term.
Start at the top
Start by tucking in the top corners of your fitted sheet; they're usually the trickiest. This makes it easier to stretch the rest of the sheet underneath the mattress.
Choose the right size
Some mattresses are deeper than others, so make sure you measure your mattress before buying new fitted sheets.
Replace worn out fitted sheets
Sometimes the reason your fitted sheet is coming off your mattress is that it’s old and the elastic has stretched. If your sheets have seen better days, it might be time for new ones.