There is nothing wrong with wearing something to give you a bit of extra confidence! Presumably if you went out on a date night you would both make an effort to wear nice clothes - if you're intending on spending a romantic evening then the same should apply to your underwear.
It really depends on your budget, and what bits you want to accentuate or possibly cover. I really rate Ann Summers lingerie - they used to be awful but over the last couple of years they've got much better. My local shop often has items on sale as well, I've picked up 3 full outfits for less than £40 before. What's really useful is that on their bodysuits, they give you a dress size and then a cup size option - for example 14 C, 14D, 14F etc. So you avoid the common problem of buying one that fits your boobs perfectly but is too tight or too loose elsewhere.
Playful Promises are also in the same price bracket, but I find their quality hit and miss.
If you've got the money for it, Agent Provocateur or Honey Birdette do some gorgeous pieces. HB sizing runs a little small IMO.
Depending on your shape, you can get some really cheap pieces on Shein. However, don't expect to be able to wash them more than once, and the sizing is generally just "S, M, L, XL" - so unless you have a "standard" figure the result can be erratic. EG I'm a DD cup and a short size 12. So if I buy a body suit that fits my boobs, I'll find the crotch is dangling around my knees, or if it fits my torso then I'll struggle to fit my boobs in.
Amazon have some good pieces, like this for example
https://amzn.to/3WolKIo
However like Shein the sizing is S, M, L etc.