That's great He doesn't sound constipated if his poos haven't got any firmer. Constipation isn't defined by how long between motions, but by the consistency of the stool. If he hasn't been in any distress or discomfort even though it was a full day between, and they weren't hard/very firm then I wouldn't be concerned about giving him potato again as soon as you want, especially if he likes it!

It's very normal for babies who have just started on solids to have stool that is almost the same as prior to starting solids, with only little bits of what they have eaten in it - they say that you can always tell what a baby/toddler has eaten for this reason! As he starts to take more solids as he gets a bit older and closer to toddlerhood, then you may see them firm up a little more (then again, you may not - some babies just always have quite wet stools, especially with the laxative effect of BM). It's very normal and nothing to worry about at this stage.

Sounds like he's doing great and really enjoying his solids, Miss E - that's wonderful!