Is it okay to use a sleeping swaddle (e.g. Love to Dream 1.0 TOG) and a blanket/muslin that's tucked into the mattress and comes up to baby's waist? Some advice I received was that to prevent SIDS, it's recommended not to have a blanket over a sleeping bag. Does this apply to sleep swaddles too?

There is no specific information in relation to any amount/type of bedding for each baby.
Generally, it is not considered necessary to use blankets when baby is in a sleeping bag as most babies are often moving around then & not staying under blanket, which may create a risk of head/face being covered.
Too much, or loose, bedding may lead to overheating as well as head/face covering.
Red Nose has the following information.

Red Nose recommend that rather than state how many bedclothes can be safely placed on a baby, parents can work out the amount of bedding to be used after considering these factors:

The room temperature where baby is sleeping.
How hot does the baby feel? A good way to check baby’s temperature is to feel baby’s back or tummy (don’t worry if baby’s hands and feet feel cool - this is normal).
Whether the baby has a cold or infection or another special need.
Consider how many layers that you as the baby’s carer are wearing comfortably.
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep