How to enable cart upsells only for one-time purchases?

[LeeB]

Trying to find a solution for a client that supports both Subscriptions AND Upsells separately.

We want cart upsells (buy more, save more) offered to customers who choose a One Time Purchase product ONLY.

We don't want upsells offered to customers who select a Subscription.

We are currently running Appstle for Subscriptions but open to changing apps if needed. So far for upsells have tested Monster, UpCart, OneClickUpsell, Cartix, PickyStory & MonkCart, but ALL show the upsell offer to customers who have selected a subscription, then if they choose the upsell offer, it removes the subscription causing customer confusion.

Any solutions/recommendations welcome! Thanks in advance.