We have two cheap potties one for upstairs and one for downstairs. We also have the toilet seat with the little steps on it in our downstairs toilet.
With my eldest we stayed in over a long bank holiday weekend and left him bottomless around the house with a potty available up and downstairs. It was a looooooong weekend but it worked and we cracked it. (he still has a few accidents now and he's 6, but that's mainly because he holds it for too long as he's busy playing
)
My 3.5 year old we started to potty train during lockdown as it was a perfect opportunity. Didn't really use the potty as he was used to seeing his brother use the seat and steps on the downstairs toilet, he's taken to it really really well (still has the odd accident and also wees on the floor from time to time
) but he takes himself for wees and poos and tells us when he needs help. We still take the potty out with us everywhere we go just in case and we have what we call a 'wee machine' that comes out with us at all times just in case.
My youngest is almost 2.5 yo but I won't even try with him till spring now when he will be 3 (or earlier if we get put into another lockdown) unless he shows strong signs he's ready!
She makes every thing into a massive drama and makes more work for herself that one!