Which reliable and easy to use paid accelerator should my heir use in case the mining fee I originally set is insufficient?
Assuming you don't plan on dying any time soon, I wouldn't worry about this yet.
Using CPFP (Child Pays For Parent) is probably better than a paid accelerator:
1. They broadcast the transaction you gave them.
2. They make a new transaction from their receiving address to a new address, with a fee high enough to pay for both transactions.