Options for storing Customer Credit Card "on file"

Hi All.

I have a client who deals with a lot of small businesses and randomly recurring orders.

What I mean by randomly recurring - In January a customer will place one order for 3 boxes, but in February they will place 5 orders for 1 box each (spread over 5 separate calls/transactions), then in March - 2 orders of 3 and 4 boxes. So it's not a subscription service and hard to predict exact amounts.

Client's customers ask them "Can you keep our CC on file", because that's apparently "common" with other vendors?

Options I came up with that will keep my client PCI-compliant:

Keep CC info in Stripe
It allows saving CC for future use, and you authenticate purchase via a token). But this requires building out a payment processing page/app that customer service agents can access, without having full-blown access to Stripe dashboard. (Requires time & $$ to build this processing page).
In QuickBooks online, they can save customer CC, and it will be encrypted for future use. This requires extra work from Accounting / bookkeeping - as each transaction needs to go via them. Also, QuickBooks Online charges about 1% more than their current CC processor (Shopify). In a low-margin business - that's a big hit.

Question:
Have I missed anything? Are there any other ways to do this?