Here's my suggestions. I will include mods ported by me and/or modified/fixed by me, some of them not available on the nexus but I will share with Gopher is he asks (all oldrim links are to be considered ported/fixed by me and so available to be shared). Weapons:
- JaySuS Swords (my ported and fixed version): tons of new and lore-friendly weapons added to the levelled list. Get them from NPCs, vendors, craft them and look for unique weapons in dungeons and other places.
- Unique Uniques: make unique weapons really unique.
- Lore Weapon Expansion: as the name say. Craft, buy or loot them.
- Warmonger Armory (my ported and modified version): this mod has the two best thief armors I have ever seen. Craft them or loot them from bandits.
- Immersive Armors Redux (my ported and modified version): it's almost the same as Immersive Armors, but I removed all scripts and edits to NPCs, I also removed lots of recepies so the armors aren't all craftable and some of them are even removed from the mod, but most of them will still appear on bandits and vendors. It's a redux version of Immersive Armors I made for compatibility reasons and because the original is way too heavy.
- B-D-Y-E-B Shield (my ported and modified version): lore-friendly shields.
- Rough Leather Armor (my ported version): cool thief armor.
- Better Leather Armor (my ported version): my ported version will replacer the vanilla leather armor. So much better.
- Interesting NPCs: the SSE version can be downloaded here. Tons of unique voiced NPCs, followers and quests! All the quests are amazing and lore-friednly and I'm sure you will find your new companion for your thief character here. To find all the quests, just ask the innkeepers about rumors. I can't raccomand playing this mod enough, it's my favorite.
- Two Handed Grimsever for Mjoll (personal mod). Mjoll is supposed to be using two handed weapons but her Grimsever weapon is a one-handed sword? Why? Well, no more!
- TM Housecarls: better Housecarls, ported by me with permission.
- Arissa - The Wandering Rogue: a thief follower, I could port it for you if you want.
- WICO (my fixed and modified version): I beg you Gopher, don't make us watch a let's play with vanilla ugly NPCs... Install this mod!
- Open Face Guard Helmets: make eye contact with the guards.
- RS Children Overhaul: no more potato head creepy children. Unique characters with a personality!
- Guards Gut Fix (my ported version): no more fat guards and stormcloaks.
- My Imperial Legion Overhaul: I will post screenshots if interested.
- Opulent Thieves Guild: better ragged flagon.
- Skyhaven Modified: it's a optional and standalone file, it makes the Skyhaven temple more useful and more pleasant, but still lore-friendly.
- Farmhouse Chimneys: you didn't notice eh? Houses don't have chimneys outside, but only inside. This mod will fix that.
- Cooking in Taverns: minor edits to taverns, it will allow you to cook food.
Quality of life:
- Equipment HUD: quick and elegant way to switch between shouts, powers and spells through hotkeys and circles.
- Five O'Clock Shadow (my ported version): let your beard grow over time! Shave it, trim it or mantein its style by clicking on the razor in your inventory!
- Animated Eating Redux: see the people of Skyrim, your followers and yourself eat more than bread! Sweetrolls!!
- Visible Favorited Gear: see your weapons, works perfectly. I play with dagger position moved to my back and with this mod I can always see my dagger on my back even when I'm using a sword.
- Khajiit Merchants Buy Stolen Items (my ported version): since you will play a thief.
- Colovian Noble Clothes - Replacer for Quest Outfits: my mod. Look unique during two vanilla quests.
- Real Feeding: be a good werewolf and finish your meals, people in Morrowind are starving.
- Better Fast Travel - Carriages and Ships - Overhauled (my ported version): carriages in all holds, towns and villages. Basically just an extended vanilla carriage system.
- INeed: eat, drink, sleep and poop! Well not the last one. Also hotkeys to eat and drink, so no need to open the menu. And your follower will eat as well.
- Rustic Clothing: HD clothes.
- aMidianBorn Book of Silence (my ported version): HD armors and weapons.
- My HD everything!! I have a 4gb archive of 2k textures from different mods I made because this part of modding Skyrim when reinstalling the game was a nightmare. The archive is SMIM compatible and includes almost all vanilla textures replaced except characters, creatures, clothes, armors and weapons. I can share screenshots if you want to take a look. Way better than vanilla.
- Vivid Weathers Definitive Edition: you don't need ENBs to make SSE look amazing. I love this weather and lighting mod.
- The Gray Cowl of Nocturnal: of course if you play a thief character, but install later in the game. Does have a HD pack downloadable here.
For last, I recommend the Skyrim Uncapper to set two perks for level if using Ordinator (or 1.5 to have 1 extra perk each two levels). I also ported Dual Sheath Redux, but it requires 1 extra step when settings things up (no big deal).
This is the best thief armor for Skyrim in my opinion (there is a male version of course): https://staticdelivery.nexusmods.com/mods/110/images/50459-1-1390942309.jpg