I don't think the later thermostat was ever fitted to the 1.1? So it's likely to be this one:
https://www.shop4parts.co.uk/?name=store&op=Product&ProdID=470 It actually fits the 60Hp 1.2 as well (ours is a 2010 60Hp 1.2 and that's the one which fits it) In fact I bought the Original Birth branded item from S4p - as part of a larger order so I could take advantage of the forum discount - I think the item with the sensor and heater takeoff pipe came in with the 69Hp VVT engine?
I did our 1.2 by removing the coils for better access. I'd read that it's recommended to remove the battery and battery tray for access but was keen to avoid disconnecting the battery in case the battery code was lost or "other problems" came about. However I'd since read, here on our wonderful forum, that the
radio code is stored in the body ECU so, as long as you keep the original fit radio, if you disconnect the battery it will automatically recognize the radio when you reconnect the battery and this is true for both our cars which have had their batteries disconnected a number of times by me when working on them - we have a 2010 1.2 Panda and a 2012 1.4 Punto in the family at this time. HOWEVER, As koalar suggests above, you are as well not to disturb wiring any more than needed, especially on the 1.1, which is known to be rather susceptible to continuity problems in the wiring to the coils so, in your particular case, probably removing the battery and tray and leaving the coils alone might be the way to go? However I've not done this job on a 1.1 so maybe someone else could advise?
Thermostat failure is something I've had on pretty much all the FIRE engined Fiats we've run - resulting in cold running of the engine - fit a new thermostat and all good again for a few years. Keep one of these cars long enough and you'll almost certainly be going to do a thermostat on it!
There have been reports of problems experienced when trying to bleed the cooling system when filling up with coolant. I've never had this problem but I do have my own wee way of doing it. If it interests you you can have a read about it here:
https://www.fiatforum.com/threads/beckys-timing-belt-all-done.459967/
Please feel free to ask anything you like as I'm sure quite a few of us will have done this job and have our own take on how best to do it. A reasonable tool kit with maybe some 3/8 drive sockets and extensions helps a lot.