A pid will give you better control over the mash.
pid such as this. I've only used the Sestos (ok) and Auber (awesome), but a REX is available cheaper but is an unknown factor
http://www.ebay.com.au/itm/DIN-Digital-PID-Temperature-Control-Controller-100-240V-12VDC-SSR-Relay-/220940409015?pt=AU_B_I_Electrical_Test_Equipment&hash=item33711318b7
Just ensure the one you choose is 240vac compatible, and has a SSR output.
Then you need 2 x SSR
http://www.ebay.com.au/itm/Solid-State-Relay-Module-SSR-25DA-25A-250V-3-32V-DC-Input-24-380VAC-Output-HP-/161080562635?pt=AU_B_I_Electrical_Test_Equipment&hash=item25812653cb
And a pt100 probe (don't use a cheaper K-type)
http://www.ebay.com.au/itm/Temperature-Control-Thermocouple-RTD-Sensor-Probe-PT100-3-WIRE-/280979584839?pt=AU_B_I_Electrical_Test_Equipment&hash=item416bb03747
Auber Instruments makes awesome probes that you can disconnect the wire completely.
And heat sinks for the SSRs.
And enclosures and wiring to connect it all up
If you really want to go the STC way, you can get SSRs that have a 240vac signal side. Then you use 1 x STC, it's probe, and feed the elements from the SSRs.
I'm even thinking mechanical relays should be ok for the stc as I don't think it switches that fast and only has a mechanical relay internally.
Your sparky mate should have a good clue of what I'm talking about.