Simplest and fastest method of utilizing Bitcoin for my online digital store?
Unfortunately, there are reasons it isn't this simple.  If it were, everyone would be doing it.

The difficulty in purchasing bitcoin online is not a technical challenge, but rather a challenge with regulations and mitigating risks.  Businesses that sell bitcoin can find themselves afoul of their local laws if they do not request a certain amount of know-your-customer (KYC) information about their customers.  There is also usually a verification process with this information, which can take time.  They can get shut down or even thrown in jail if they don't comply.

Secondly, bitcoin transfers can't be reversed...but PayPal and credit card transactions can be.  This means that if you purchase bitcoin with either of these methods, the company selling you the bitcoin will need to wait until you can't do a chargeback on your purchase.  Depending on your method of payment, this can take weeks.  It's what bitcoin sellers need to do in order to protect themselves from fraud.

Bitcoin, itself, offers a payment method that is secure, convenient, trustworthy, and quick.  However, the on-ramps and off-ramps from fiat currencies to bitcoin have all the slowest and most inconvenient elements of the legacy currency system.