Or you could wear layers in something that you love and feel great in - you might be going to an Italian wedding (I bet the views and the food will be amazing!), but if you are British why not dress in something that you love?
We British (sorry if my assumption that you are British is wrong, but apart from that I still think you should wear something you love) might not be known as elegant and enthusiastic followers of fashion, but we can look just as stunning as our Continental neighbours!
Of course I can appreciate a tall, slim, elegantly dressed woman, but with my measurements not only would I look ridiculous in the sorts of clothes they wear, I would be going against my own taste in clothes, and if I didnt feel great in myself it wouldn't matter if I was wearing a €3500 cashmere dress suit in an understated dark colour with matching accessories, and a fine 22 carat gold chain around my neck with tiny matching earrings, I would still just look like someone who was trying too hard, but had no idea what looked good on them!
So, you will have a toddler with you, and you will be somewhere that will in all likelihood be very cold outside, but heated inside? Unless you know that you are going to be in a marquee for most of the time after the church wedding, you really will need to be dressed in layers, as will your toddler. When you are inside at the reception you will probably spend an unreasonable amount of time chasing after an over excited toddler (hopefully most Italians live up to their reputation and adore children, if so you might get some help entertaining/running after your delightful toddler!) Therefore, as you are no doubt well aware, you will need to be wearing something with a lot of 'give' in it, that will not have any embarrassing body part accidents, and yet can be stripped down to the bare minimum (without the bare 😁) when you get far too hot, but can be layered up again if you go out into the gorgeous gardens for photos, or just for some fresh air!
Sorry OP, I have no actual clothing suggestions for you (and embarrassingly I don't know how to do links anyway), except for your tights (I presume with a toddler in tow that you won't be wanting to spend some "quality time" with a gorgeous young Italian stallion whilst at the actual reception, as otherwise tights might not actually be the way you want to go... 🤭). I suggest Snag tights as they come in a wide range of sizes, have loads of different colours, and most of them come in at least two different weights. I think 80 denier might be a good compromise for where and when you will be there, and they are made in Italy!
Whatever you end up wearing Serenissima - layers, relax and have a great time with your toddler. If you feel happy and confident in yourself then I think you will look stunning, and if any of the other guests look down on you - and I doubt very much that they would - that would say loads about them, and how shallow (and probably uncomfortable) they are, and nothing about how amazing you look! 🍾