I’ve tried nude yoga at home and found I could do more than I could when wearing clothes, even loose fitting gym kit.
The gym I go to (extremely rarely) doesn’t currently do nude sessions unfortunately but it recommends working naked at home as a good way of seeing which muscles are being exercised.
I totally agree on the significantly improved flexibility that nudity gives over even loose-fitting and quite minimalist clothing. After my first few sessions of yoga I felt like I’d found some muscles I never knew I had, because they ached. Perhaps your gyms advice would have been good to have heeded, so I might have had a head-up as to where I might ache.