Swimming can be useful in some situations (egg bound females, impaction) but for the most part, if you’re just soaking it’s always best they be able to have something to hold onto for security.
Another low stress option that is easier than upping the entire enclosure humidity is to offer a humid hide with damp sphagnum moss during shed cycles. That said, 78-90% humidity for sustained periods is going to give you issues with air quality, which could lead to RIs. Here’s some previous advice on humidity levels and sheds from a past thread: