From my quick look at industry standards, your original format is the most popular size - poetry books go for a more intimate feel and so even though it will be thicker, the overall 'small' feel to it should still be appealing. I also agree with Rob, that keeping to the same size as your original work is important because it looks better on a bookshelf when readers collect the series. My first novel is substantially thicker than my second, but trim-wise they are both the same and there have been no issues with that. Here are a couple of websites I came across with more information, which you may or may not have seen before. Good luck with the project!

https://www.morethanjustprint.co.uk/printing-tips-advice/standard-uk-book-sizes/

https://www.ingramspark.com/blog/what-to-consider-when-publishing-poetry