@Alex thank you! Where did you buy the training pants from?
You can get them from Amazon if you need them quickly but we got ours from https://www.rudiebaby.co.uk/products/training-diapers?variant=41091300065340 They regularly do great deals.
Knickers or underpants. We used training pants as they are knickers with 6 layers in the gusset lining to prevent leaks if our daughter had an accident.