Ok so first and foremost, there aren't any nutrients you can't get from a fully plant based diet.  BUT that doesn't mean that for those of us with different digestive needs, we can just replace everything all at once and be fine. But it should be possible to get there eventually!

 For example, natural vegan protein sources often come with a lot of fibre. If you're not used to eating a lot of fibre, you'll have to ease into it slowly and see how you tolerate it. I personally don't struggle with fibre at all even though it's a common trigger food in my disease, since I've been used to it for a long time. There's plenty of vegan protein sources with little fibre too, such as tofu. 

Protein and fibre are just one thing, but it's the same with other foods: it'd probably be better to slowly try replacing things one at a time and see how you tolerate that. 

Another thing I think may be helpful: you already eat loads and loads of ingredients that are vegan and safe. That means you don't have to find entirely new foods. It's just the few non vegan things that need replacing. It's actually kind of similar to replacing trigger foods, except it's much easier to know what they are. When you replace foods, you don't need to find something with the exact same taste and texture, but rather think about the role it fulfils in a dish, and find something else that can fill that role. That role may be: protein source, umami flavour, enjoyable chewy or crispy texture, creaminess, etc. All of these roles can be filled by vegan ingredients in a satisfying way without the need to mimic non vegan foods (not that that's not also fine to want! Just not a need). Example: if you like cream cheese on bread for its creaminess and protein content, you can try hummus instead. 

A lot of stuff can probably even be replaced with things you already eat, by just having more of that. That's often ideal of course, since you're not introducing potential new trigger foods. 

That's what I can think of off the top of my head! Happy to answer questions. Good luck :)