Bottom lifting knickers for a dress ahead of a weekend away?

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Big 50 in 2 weeks!
Weekend away planned,can finally fit in dress I've waited 4 years to get into!!!
But my bum looks seriously droopy in it!😕
I know the only real solution is glutes exercises but that's not going to make a big enough difference in 2 weeks.
Can anyone recommend bottom lifting knickers? Need to be seamless due to material and fit of dress.
I'm looking for personal recommendations as I don't trust the companies product reviews.
I've seen underwear with pads on hips and rear but I don't need anything to look bigger!!
I just want a Wonderbra for my bum!

Oh and budget friendly!
I can't afford to spend £100 on knickers on top of the weekend away!

I have some of these from h&m

https://www2.hm.com/en_gb/productpage.1316291002.html www2.hm.com/en_gb/productpage.1316291002.html]]]]

I actually wear them more for warmth and modesty under thin dresses rather than lifting. But they do have a lifting and smoothing effect. Probably not as much as Spanx would, but enough for me and not so tight as to be uncomfortable.

Otherwise I’d take a look at Spanx or the Kardashian ones (Skims?) but they will be pricier.