Enforce increase of vector capacity by implementation defined factor when reserving

Question

So I have a class wrapping a vector which has the invariant that vec.capacity() > vec.size() so I can always (temporarily) emplace_back one more element without reallocation. My first idea was to call vec.reserve(vec.size() + 1) for every insertion, but this is inefficient as seen in this stackoverflow thread, and insert is called very often. (So is pop_back, therefore the maximal number of elements is way lower than the amounts of insert calls.)

My current implementation simplified looks something like this:

#include <vector>

template<typename T>
class VecWrapper {
private:
    std::vector<T> vec;

public:
    [[nodiscard]] auto insert(T new_element)
    {
        vec.emplace_back(std::move(new_element));
        if (vec.capacity() == vec.size()) {
            vec.emplace_back(vec.back());
            vec.pop_back();
        }
    }
};

Is there a less awkward way to trigger a capacity expansion of the vector according to the implementation defined strategy? Note that T is not necessarily default constructible.