To be honest with you I didn’t answer before this because I wasn’t confident on the velvet bolero. I guess try it on and if the blacks match and it doesn’t look too weird, then it works? There’s nothing that says velvet can only be worn with velvet, it’s more whether the sleeves match up, or the bolero just looks like shit on you (I also have a 95cm bust and sometimes the stretch boleros don’t work out)
Legwear, you can buy plain black tights, either thermal or high denier ones, from Gu or Uniqlo. Gu/Uniqlo is pretty cheap and decent quality. You can also pick up some thick shorts here, which will keep you warmer than cotton bloomers, as well as a woollen stole or something if you need it — you can buy a fancy pin from either Gu or closet child and use that to dress up the shawl, at least you’re covered and warm.
Assuming Harajuku closet child, you can easily find red, wine or bordeaux accessories pretty easily, also jewellery from aatp, Moitie, Chocomint to add some polish to the coord. At the very worst, they always seem to have a basket of plain black headbows and a rack of outerwear that you can buy warmer stuff from, if the bolero doesn’t work out.
Actually I’m pretty sure if any of your pieces don’t work out you can pretty much put together a whole coord from closet child, only the shoes might be a bit of a gamble (They have a lot of variety, but you won’t necessarily find the right combination of size, colour and style). I’d try closet child before going to Gu for this reason, you have a pretty good chance of finding legwear that matches your dress at closet child (whether it warm enough is another story though).
If using a different secodhand shop, still pretty much the same advice, but it’s more of a gamble. I think Usagiyouhinten has much lower chances of finding a basket of black accessories, but they do carry some more obscure homemade indie accessories.