If you want a profession combo that can do well both in TBC and WotLK, well…
As a resto shaman, anything goes for WotLK. The main stat you’ll stack up in WotLK will be spellpower, so any profession with a spellpower static bonus (Blacksmithing, Enchanting, Leatherworking, Inscription [but I’m not gonna count this one since you don’t wanna change profs apparently], Jewelcrafting and Alchemy) are all valid choices.
Things change if you’re an elemental or enhancement shaman. Both specs, in WotLK, have cooldowns in the forms of class abilities and trinkets (especially Enha) that you want to take advantage for. Furthermore, both specs can have a need to focus on stats other than spellpower/attack power. Early on, WotLK Elem wants to stack a lot of crit iirc, and WotLK Enha stacks up haste until really late into the game (or begins stacking haste once rly late into the game, I never remember which one it is). This means that (1) proc-based or cooldown-based professions (Tailoring and Engineering) suddenly become much better and (2) as far as static bonus professions, you want those with flexible bonuses (such as Blacksmithing’s extra sockets and Jewelcrafting’s epic gems). With that being said, I’d suggest:
Enhancement: Blacksmithing is a strong choice in both TBC (crafted weapons) and WotLK (flexible stat bonuses). As a secondary profession, Leatherworking offers you a strong advantage in TBC (yes, drums) but is still serviceable in WotLK, while Jewelcrafting is minor in TBC but offers you more flexibility in WotLK. If you wanna maximize your TBC performance, I think Leatherworking/Blacksmithing is the way to go, while Tailoring/Engineering would be the strongest WotLK combo.
Elemental: Pretty much the same as for enha, except that Blacksmithing is useless for TBC Elem. The advantage though is that the only thing you rly need for TBC is Leatherworking, and that’s still a strong choice for WotLK (especially past tier 7). Enchanting gives you a nice SP boost both in TBC and in WotLK. Again, Tailoring and Engineering would prolly be optimal in WotLK, but Elem is less dependant than Enha on big cooldowns, so you may be fine just using LW/Ench even in WotLK (to be fair, elem isn’t very competitive in WotLK PvE to begin with, so yeah).
Restoration: If you intend to play both TBC and WotLK at top level in PvE, this is prolly the spec you’re looking for. Thankfully, unlike Enha and Elem, Resto doesn’t rly need cooldowns/procs from professions, so you can just pick any prof in TBC that gives you a static boost in WotLK. As a result, Leatherworking is a no-brainer and either Enchanting or Alchemy are valid secondary choices (with Enchanting having a slight edge due to more utility in TBC, but in WotLK the two profs are pretty much equivalent in terms of PvE advantage). Tailoring can be useful in TBC early on, but becomes eventually obsolete and would be kinda substandard in WotLK.
One last note, though, is that profession choice (for shaman, at least) is much more impactful in TBC than it is in WotLK and, with the only possible exception of Engineering for WotLK Enha (a must if you wanna be serious/competitive), anything goes kinda. So, I’d say you should base your prof choices more on TBC than on WotLK.