2 elements and 2 SSRs will work fine as long as only one is powered at a time.
You could use a DPDT ON-OFF-ON toggle switch to select either kettle ON, both OFF, or MLT ON. The switch will need to handle 25A at 220v.
Alternately, you could use a toggle or rotary switch to control the coil to two AC contactors, one for each element. An e-stop could also be wired to easily disable both contactors. See kals design on theelectricbrewer.com for details.