A cold bed and 3M blue painters tape cleaned with alcohol provides me with great PLA adhesion. I've broken multiple prints and pieces of glass with this approach. If I have a delicate part or a very large print, I'll cut back on the alcohol swabbing so that wax on the tape limits the adhesion.

Make sure your clips are close to the bed corners. The farther they are from the corners, the less degree that the glass is mechanically tied to the bed mounts in the corners.

It's not the mechanical relay that is the problem here. The root issue is that the (glass + heat bed) flexes as heat is turned on and off. A mechanical relay requires the heat to be turned on and off fairly slow, leading to the flex being detectable in some prints. Swapping out the mechanical relay with a Solid State Relay (SSR) allows you to then migrate to PID, a smarter control method built into Marlin that turns heat on and off far faster. The faster cycling both provides a more stable temperature and won't lead to as much noticeable flex. It takes the combination to reap the benefits. Just swapping out the relay alone won't solve the problem.

For more info, you can search the MakerFarm subforum for Solid State Relay. Here's one recent thread - 3dprintboard.com/showthread.php?15818-How-I-fixed-Z-banding-on-my-12-quot-i3v-AL-Y-bed-and-solid-state-heat-bed-relay-PID