Well porter_jamie’s friend may well have insider knowledge so worth looking into! Sometimes there is a lemon in the range. There should be some good reviews about.
Maybe check out Parkers guide online and have a look at small cars in that come into your price range? Maybe a Fiesta will be good? My brother just bought one, 08 1.4 3 door job, square body shape not the new one. Its a really nice car. 6K though.
I would avoid a Corsa TBH, my ex had a 1.2 (02) and it’s horrible!
If you are worried about a 1.2 being underpowered a 1.2 in any car will be sluggish, esp if you have been driving 1.4 and 1.6 cars. Maybe a 1.4 will be one to go for? Will be loads better on the M way.