Welcome to the forum
@Bevs
There is experience of a variety of pumps to tap Into on here.
like you I had a Combo, and was happy with that for eight years before switching to a 780G.
I used it alongside the Libre, but was not able to use the Sensor readings in place of BGs at meals, or do corrections without putting a Bg in (I know that that is a good safety feature, but there were times when I did not feel I needed a BG)
I was advised that there was no advantage in using a 640 since if I had a 780 and used it in manual mode with or without the sensors, it acted in the same way as a 640. However in addition the 780 gave me the option of the autocorrections by the pump every 5 minutes in a closed loop. I chose that option and self fund my sensors to run the closed loop system.
I found the change over very difficult with a variety of factors making it a bit of a bumpy ride (Illness, Brexit delays, COVID vaccines, kidney stones, ....), but I think I would have found any change over quite difficult. Now I am finding it has reduced the amount that I have to think about. If I get the carbs a bit out, the pump will sort it out, I sleep really well knowing that I will have a good flat line overnight. I still need to do a BG at each meal and before bed to calibrate the sensor, but in doing that I avoid most interruptions/alarms apart from those when I go low. However I used to have a couple of hypos each day. I now have one or two each week, and my time in range is usually in the 80s or 90s. There are still those weird days when things just don’t make sense, but they seem to settle quite quickly.
I hope that helps