Whoa!!
Without knowing anything about the particular laptop (or motherboard or CPU), everyone here is just guessing - and sadly, not always offering correct information.
I know this wouldn't be an option with DDR4
That's not true. Again, it depends on the laptop (more specifically, the motherboard/chipset and CPU). And sadly, you told us nothing about this laptop, other than it runs 2 x 16GB of DDR5.
If you mix them, it won't run in dual channel anymore.
Again, it depends on the motherboard.
At this point in time, all we know is this laptop [apparently] has 2 RAM slots populated with 16GB sticks. It should be noted that some modern processors/chipsets/boards can support different size sticks in mixed modes with no problems. That is, access will run in dual channel up to the capacity of the lowest memory stick, then single-channel afterwards.
Some motherboards will not support dual channel unless the sticks are the same size. Same speed is no longer necessary with modern systems and I have to assume since it supports DDR5, it is modern. If different speeds, the speed of the slowest stick will be used.
That said, it is critical to note in almost every case, more RAM trumps faster RAM. So, if I was looking to improve performance by adding RAM, but did not have the budget for total RAM upgrade, I would not hesitate to run 48GB (1 x 16GB + 1 x 32GB) in single channel as that undoubtedly
has the potential to offer significant performance gains over 32GB (2 x 16GB) in dual channel.
Do note that while dual-channel does improve performance, it does not come close to doubling performance as marketing hype often suggests.
should be more then enough for all my current needs?
I guess we are expected to be mind readers and already know your current needs.
This leads me once again to point out that everyone thus far is just guessing.
So, we have no clue what your current or future needs are or will be. With that being said, depending on those needs (and your current hardware - which we know nothing about), it should be pointed out that 32GB is already a HUGE amount of RAM!
"IF" your current notebook has, for example dedicated graphics RAM for an integrated graphics solution, or better yet, a graphics card as some of the better notebooks do, AND if your notebook uses a SSD instead of a hard drive, it is very possible you will NOT "see" any performance gains by adding more RAM during your real-world use and therefore would just be wasting your money. That is why I said above, adding more RAM only "
has the potential" to improve performance. It may not - except on paper (benchmark scores).
Also,
if me, and I was set on upgrading my RAM, I would not do so until I built up my budget to fully upgrade and buy both sticks all at once. I would NOT buy 1 stick today, then hope to find and buy a matching stick later on down the road. You may be planning to purchase a 2nd stick in 2 or 3 months but life (and unexpected expenses) has a tendency get in the way of the best laid plans. If it ends up being 12 months instead of 2, a matching stick may not be available.